ITT we are discussing Open Broadcaster Software, A.K.A. OBS. I will be using this thread to document my usage of this software for live streaming and video recording. Readers are invited to ask questions, share tips, and generally discuss the application.
This post is a work in progress.
I would like to try streaming using OBS sometime soon.
My main use so far is for recording streams and other video sources and I really am impressed by the versatility of OBS in this regard.
Since YT adopted changes to prevent my Firefox extension from downloading audio/video from them, I have found this FOSS indispensible. Sure, the ads cannot be blocked, but I just press pause on the recording and then resume recording when appropriate to do so.
It’s very good.
YT adopted changes to prevent my Firefox extension from downloading audio/video
Use yt-dlp.
the ads cannot be blocked
Use Ublock.
As I have been using the ‘browser’ native to OBS, which does not accomodate extensions like uBlock, I have suffered through the ads.
I will work on recording the stream through Firefox which I do have uBlock enabled on.
Did I try that before and failed? Can’t remember. Worth giving a go in any case.
My version of Debian doesn’t support browser source. Did you install from Flatpak? Different machine? Looked back? 
Yes I installed from Flatpak.