I have the same issue, but the pavucontrol trick does not do it for me
as I have only one microphone (the one of my webcam on my laptop) and
it's not muted.

ungoogled-chromium complains about an "Error obtaining microphone permission."

Note that both the webcam and the microphone work in other contexts
(e.g. audacity, appear.in).

-- 
Pierre Neidhardt
https://ambrevar.xyz/