I don’t think you bypass the age checks with the alternative front-ends? I’ve been using FreeTube for some time, and whenever there has been an 18+ video, I would not be able to view it as I would not pass the age check. If this is a more general check that is being rolled out, I guess there will be less and less videos that will work through these.

I think I need to start hoarding video tutorial series and self-host them. Would something like TubeArchivist be my best bet for that?

Oh, this was a general issue? It was driving me crazy as I was certain I hit “shut down” instead of “reboot”. I am soon getting a Linux laptop at work anyway (I’ve only been waiting about 5 montha for it now, so any day now!) - so I will hopefully not experience this fix.

You can export your data from Spotify, and use that as a basis for downloading songs via for example yt-dlp (this can be automated), or slowly build it up again over time in whatever system you set up by buying the albums/compilations containing the songs.