Others can’t hear us

Yes. This one - jitsi-meet-release-notes/CHANGELOG-WEB.md at master · jitsi/jitsi-meet-release-notes · GitHub

If this is an upgraded setup, there may be some old config files which cause some problems.
Is this a newly fresh setup?
What are your distro and the prosody version?

Are you using preJoin screen?

Fully fresh setup specifically to avoid intervening from any old config

Ubuntu 20.04.3 LTS
jicofo 1.0-832-1
jitsi-meet 2.0.6726-1
jitsi-meet-prosody 1.0.5675-1
jitsi-meet-turnserver 1.0.5675-1
jitsi-meet-web 1.0.5675-1
jitsi-meet-web-config 1.0.5675-1
jitsi-videobridge2 2.1-595-g3637fda4-1

No, we are not using preJoin screen

Try enabling preJoin, that should help.

That should HELP, or should FIX the problem? According to this - Sometimes participants can't hear other participants · Issue #5230 · jitsi/jitsi-meet · GitHub - preJoin screen didn’t fix it. Or maybe I’m mixing two different problems?

That fixes one of the known problems, the one that you need a user action to play video elements on the page … I haven’t seen client logs from a problem session, so I’m guessing what can be the problem.

Update: We’ve enabled preJoin screen and it seems to make a situation better, but it was not fixed. During last three days we’ve had 3 major meeting with 15-20 participants and there was 1 time when someone couldn’t hear all others until his browser page was reloaded once. We’ve tried to switch to meet.jit.si and the very first meeting gave us 1 participant who couldn’t here anyone until he reloaded his web-page 2 times.