To reproduce, open a site that requests microphone permission, e.g. https://meet.jit.si/agl. The application UI will report an error: "cannot access microphone", and there is no way to give the microphone permission to the site through the browser UI.

This is the log reported while this operation happens:

Nov 12 11:46:09 raspberrypi3 systemd[1]: Started Multimedia Service for user 1001.
Nov 12 11:46:09 raspberrypi3 audit[835]: AVC lsm=SMACK fn=smack_inode_permission action=denied subject="System::Pipewire" object="User::App::browser" requested=x pid=835 comm="pipewire" name="684" dev="proc" ino=24284
Nov 12 11:46:09 raspberrypi3 audit[835]: SYSCALL arch=40000028 syscall=322 per=800000 success=no exit=-13 a0=ffffff9c a1=7ececd04 a2=a4900 a3=0 items=0 ppid=1 pid=835 auid=4294967295 uid=1001 gid=1001 euid=1001 suid=1001 fsuid=1001 egid=1001 sgid=1001 fsgid=1001 tty=(none) ses=4294967295 comm="pipewire" exe="/usr/bin/pipewire" subj=System::Pipewire key=(null)
Nov 12 11:46:09 raspberrypi3 audit: PROCTITLE proctitle="/usr/bin/pipewire"
Nov 12 11:46:09 raspberrypi3 audit[835]: AVC lsm=SMACK fn=smack_inode_permission action=denied subject="System::Pipewire" object="User::App::browser" requested=x pid=835 comm="pipewire" name="684" dev="proc" ino=24284
Nov 12 11:46:09 raspberrypi3 audit[835]: SYSCALL arch=40000028 syscall=322 per=800000 success=no exit=-13 a0=ffffff9c a1=7ececd04 a2=a4900 a3=0 items=0 ppid=1 pid=835 auid=4294967295 uid=1001 gid=1001 euid=1001 suid=1001 fsuid=1001 egid=1001 sgid=1001 fsgid=1001 tty=(none) ses=4294967295 comm="pipewire" exe="/usr/bin/pipewire" subj=System::Pipewire key=(null)
Nov 12 11:46:09 raspberrypi3 audit: PROCTITLE proctitle="/usr/bin/pipewire"
Nov 12 11:46:09 raspberrypi3 pipewire[835]: [E][000000343.735326][module-access.c:89 check_flatpak()] failed to open "/proc/684/root": Permission denied
Nov 12 11:46:09 raspberrypi3 pipewire[835]: [W][000000343.735526][module-access.c:164 core_check_access()] module 0xc85700: client 0xc87d58 sandbox check failed: Permission denied
Nov 12 11:46:09 raspberrypi3 pipewire[835]: [E][000000343.737527][module-access.c:89 check_flatpak()] failed to open "/proc/684/root": Permission denied
Nov 12 11:46:09 raspberrypi3 pipewire[835]: [W][000000343.737656][module-access.c:164 core_check_access()] module 0xc85700: client 0xc9a6b8 sandbox check failed: Permission denied
Nov 12 11:46:09 raspberrypi3 kernel: audit: type=1400 audit(1573559169.896:12): lsm=SMACK fn=smack_inode_permission action=denied subject="System::Pipewire" object="User::App::browser" requested=x pid=835 comm="pipewire" name="684" dev="proc" ino=24284
Nov 12 11:46:09 raspberrypi3 kernel: audit: type=1300 audit(1573559169.896:12): arch=40000028 syscall=322 per=800000 success=no exit=-13 a0=ffffff9c a1=7ececd04 a2=a4900 a3=0 items=0 ppid=1 pid=835 auid=4294967295 uid=1001 gid=1001 euid=1001 suid=1001 fsuid=1001 egid=1001 sgid=1001 fsgid=1001 tty=(none) ses=4294967295 comm="pipewire" exe="/usr/bin/pipewire" subj=System::Pipewire key=(null)
Nov 12 11:46:09 raspberrypi3 kernel: audit: type=1327 audit(1573559169.896:12): proctitle="/usr/bin/pipewire"
Nov 12 11:46:09 raspberrypi3 kernel: audit: type=1400 audit(1573559169.896:13): lsm=SMACK fn=smack_inode_permission action=denied subject="System::Pipewire" object="User::App::browser" requested=x pid=835 comm="pipewire" name="684" dev="proc" ino=24284
Nov 12 11:46:09 raspberrypi3 kernel: audit: type=1300 audit(1573559169.896:13): arch=40000028 syscall=322 per=800000 success=no exit=-13 a0=ffffff9c a1=7ececd04 a2=a4900 a3=0 items=0 ppid=1 pid=835 auid=4294967295 uid=1001 gid=1001 euid=1001 suid=1001 fsuid=1001 egid=1001 sgid=1001 fsgid=1001 tty=(none) ses=4294967295 comm="pipewire" exe="/usr/bin/pipewire" subj=System::Pipewire key=(null)
Nov 12 11:46:09 raspberrypi3 kernel: audit: type=1327 audit(1573559169.896:13): proctitle="/usr/bin/pipewire"
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.064051][device.c:541 device_add_object()] device 0xcc01c8: missing factory name
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [E][000000344.080573][alsa-pcm.c:37 spa_alsa_open()] open failed: No such device
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.080670][adapter.c:175 find_format()] adapter 0xcc5d20: no format given
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [E][000000344.080733][module-adapter.c:208 create_object()] usage: node.name=<string>
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.081001][device.c:541 device_add_object()] device 0xcd3ff0: missing factory name
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.086712][device.c:541 device_add_object()] device 0xcdbda8: missing factory name
Nov 12 11:46:10 raspberrypi3 kernel: vc4_hdmi 3f902000.hdmi: ASoC: can't open interface 3f902000.hdmi: -19
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.093981][device.c:541 device_add_object()] device 0xcdbda8: missing factory name
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [E][000000344.101722][remote.c:129 core_event_error()] remote 0x102c010: object error 0: seq:6 -22 (Invalid argument): usage: node.name=<string>
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.138171][connection.c:147 connection_ensure_size()] connection 0x1041b48: resize buffer to 29872 4112 65536
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.181349][connection.c:147 connection_ensure_size()] connection 0xcad978: resize buffer to 29016 4112 65536
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.196114][connection.c:147 connection_ensure_size()] connection 0xcad978: resize buffer to 32768 1888 65536
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.202963][connection.c:147 connection_ensure_size()] connection 0xcad978: resize buffer to 61480 4112 98304
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.224488][connection.c:147 connection_ensure_size()] connection 0x1041b48: resize buffer to 32768 16 65536
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.231104][connection.c:147 connection_ensure_size()] connection 0x1041b48: resize buffer to 65536 2080 98304
Nov 12 11:46:10 raspberrypi3 wireplumber[841]: Could not find target endpoint
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.508889][connection.c:147 connection_ensure_size()] connection 0xcad978: resize buffer to 94400 4112 131072
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.550154][connection.c:147 connection_ensure_size()] connection 0xcad978: resize buffer to 127224 4112 163840
Nov 12 11:46:10 raspberrypi3 wireplumber[841]: role 'Music' not found in endpoint
Nov 12 11:46:10 raspberrypi3 pipewire[835]: Hardware PCM card 0 'bcm2835 ALSA' device 0 subdevice 0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: Its setup is:
Nov 12 11:46:10 raspberrypi3 pipewire[835]: stream : PLAYBACK
Nov 12 11:46:10 raspberrypi3 pipewire[835]: access : MMAP_INTERLEAVED
Nov 12 11:46:10 raspberrypi3 pipewire[835]: format : U8
Nov 12 11:46:10 raspberrypi3 pipewire[835]: subformat : STD
Nov 12 11:46:10 raspberrypi3 pipewire[835]: channels : 2
Nov 12 11:46:10 raspberrypi3 pipewire[835]: rate : 48000
Nov 12 11:46:10 raspberrypi3 pipewire[835]: exact rate : 48000 (48000/1)
Nov 12 11:46:10 raspberrypi3 pipewire[835]: msbits : 8
Nov 12 11:46:10 raspberrypi3 pipewire[835]: buffer_size : 65536
Nov 12 11:46:10 raspberrypi3 pipewire[835]: period_size : 1024
Nov 12 11:46:10 raspberrypi3 pipewire[835]: period_time : 21333
Nov 12 11:46:10 raspberrypi3 pipewire[835]: tstamp_mode : ENABLE
Nov 12 11:46:10 raspberrypi3 pipewire[835]: tstamp_type : MONOTONIC
Nov 12 11:46:10 raspberrypi3 pipewire[835]: period_step : 1
Nov 12 11:46:10 raspberrypi3 pipewire[835]: avail_min : 1024
Nov 12 11:46:10 raspberrypi3 pipewire[835]: period_event : 0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: start_threshold : 2147483647
Nov 12 11:46:10 raspberrypi3 pipewire[835]: stop_threshold : 65536
Nov 12 11:46:10 raspberrypi3 pipewire[835]: silence_threshold: 0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: silence_size : 0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: boundary : 1073741824
Nov 12 11:46:10 raspberrypi3 pipewire[835]: appl_ptr : 0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: hw_ptr : 0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.700728][node.c:1303 node_ready()] node 0xcdfc30: graph not finished
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.700852][node.c:777 dump_states()] node 0xcb5550 (audio.convert/api.alsa.pcm.sink/alsa_card.platform-soc:audio/Multimedia): pending:0/2 s:344681889059 a:344682073382 f:344682349736 waiting:184323 process:276354 status:3 sync:0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.700898][node.c:777 dump_states()] node 0xce62a0 (ALSA plug-in [AudioThread]): pending:0/1 s:344680611716 a:344680687913 f:344681872809 waiting:76197 process:1184896 status:3 sync:0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.700937][node.c:777 dump_states()] node 0xcdfc30 (api.alsa.pcm.sink/alsa_card.platform-soc:audio): pending:-4/6 s:0 a:0 f:344680521143 waiting:0 process:344680521143 status:3 sync:0
Nov 12 11:46:10 raspberrypi3 pipewire[835]: [W][000000344.700969][node.c:777 dump_states()] node 0xcdfc30 (api.alsa.pcm.sink/alsa_card.platform-soc:audio): pending:-4/6 s:0 a:0 f:344680521143 waiting:0 process:344680521143 status:3 sync:0
Nov 12 11:46:15 raspberrypi3 pipewire[835]: [W][000000349.224894][node.c:343 suspend_node()] node 0xce7170: error unset format output: Input/output error
Nov 12 11:46:15 raspberrypi3 pipewire[835]: [W][000000349.225216][node.c:343 suspend_node()] node 0xce7170: error unset format output: Input/output error
Nov 12 11:46:15 raspberrypi3 wireplumber[841]: role 'Music' not found in endpoint
Nov 12 11:46:15 raspberrypi3 pipewire[835]: [W][000000349.242689][node.c:343 suspend_node()] node 0xce62a0: error unset format output: Input/output error

FTR, I tested a Raspberry Pi 3 and a USB camera with microphone. This is the log when plugged:

Nov 12 11:42:29 raspberrypi3 kernel: usb 1-1.4: new high-speed USB device number 5 using dwc_otg
Nov 12 11:42:29 raspberrypi3 kernel: usb 1-1.4: New USB device found, idVendor=1415, idProduct=2000
Nov 12 11:42:29 raspberrypi3 kernel: usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
Nov 12 11:42:29 raspberrypi3 kernel: usb 1-1.4: Product: USB Camera-B4.09.24.1
Nov 12 11:42:29 raspberrypi3 kernel: usb 1-1.4: Manufacturer: OmniVision Technologies, Inc.
Nov 12 11:42:29 raspberrypi3 kernel: usb 1-1.4: current rate 1659 is different from the runtime rate 16000
Nov 12 11:42:29 raspberrypi3 kernel: usb 1-1.4: 3:1: cannot get min/max values for control 2 (id 3)
Nov 12 11:42:29 raspberrypi3 kernel: gspca_main: v2.14.0 registered
Nov 12 11:42:29 raspberrypi3 kernel: gspca_main: ov534-2.14.0 probing 1415:2000
Nov 12 11:42:32 raspberrypi3 kernel: usbcore: registered new interface driver ov534
Nov 12 11:42:32 raspberrypi3 systemd-udevd[670]: Process '/usr/sbin/alsactl restore 2' failed with exit code 99.