@GiovannettiAntonio-4409 thank you for raising this feedback. Do you perhaps have i3 WM? In 1.3.00.16851 we introduced screensharing red border indicator and we noticed that on i3 it causes issues with transparency.
Symptoms would be black screen with red border. If you do have this, can you try to rename this file (so it is not used)
/usr/share/teams/resources/app.asar.unpacked/node_modules/slimcore/bin/rect-overlay
and try again?
We are working on the fix on our side.