I’ve looked around for a feature that resembles Skype’s nice lady that checks your connection and plays back whatever you tell her so you know your mic output is being picked up.
Is there such a thing somewhere or a plugin or…?
It came up over here with the Janus WebRTC dev (GitHub - meetecho/janus-gateway: Janus WebRTC Server) giving his ideas for a start: LNXMuSCNS video meet April 3rd / 6pm GMT / 8pm CEST / 14.00 EDT - LinuxMusicians
*edit:
his suggestion is to launch Chromium with
--use-fake-ui-for-media-stream --use-fake-device-for-media-stream --user-data-dir=/tmp/fakechrome --no-first-run
Welcome to the forum.
Well, not a play back, but yes, there’s a mic test feature in ‘Settings’. The meter will show if your mic is working and how loud it is.

thanks @Freddie, hadn’t noticed that at all… 
just thinking aloud here and perhaps overkill since Freddie pointed out there’s an input meter in the meet settings but anyway…:
the ‘bot’ user is host for the meet
guest users are informed beforehand to speak one at a time
or the bot shares an image or gif informing about it
bot host runs a 5 second overdub loop recorder and sends the output of the loop back to the meet
if a guest user speaks for 5 seconds it is repeated back to him during the next 5 seconds
to avoid cacaphonic feedback layered recordings:
a macro or programmable function mutes the bot host’s mic every 5th second and unmutes it again every 5th second