PSA: if Google Meet doesn't have working screen-sharing for you in Chromium on Debian, change your user agent (in DevTools -> Network Conditions) to Microsoft Edge (Chromium) and it works.

this happens due to an anticompetitive measure by Google, namely the forced use of the Google-specific Hangouts extension by Meet screensharing on non-Edge-branded Chromium

@whitequark is this new? we've been screensharing from chromium in meet just fine for the past year
@artemis it's specifically the Debian Chromium that's broken here due to this line: https://sources.debian.org/src/chromium/112.0.5615.138-1~deb11u1/debian/rules/#L79
File: rules | Debian Sources

@whitequark ah yeah. checking my USE flags

+ + hangouts : Enable support for Google Hangouts features such as
screen sharing

there it is