I self-host some things because I like the technical challenge, and what I've found is that the effort required to maintain the online presence of the data is quite demanding. Less so if it's outsourced, but without actively 'tending the garden', it will inevitably disappear at least from the public-facing internet.
The ephemerality is also exacerbated by Google / Facebook account terminations.
We could have had so many nice things if it wasn't for those things.
It's almost as if there's somewhere a country which acts as a fertile breeding ground for these uncontrollable unregulated monstrosities, to grow really big, and at some point left roaming wild for other countries to deal with "yeah we don't do that here" (by which I mean stuff like false advertising and reasoning like "if it's legal and I make a profit then I get to do it").
Personally I've started locally saving anything I think I would want to watch or reference again. When favoriting something or saving it to a playlist, I download it too. I started off with using youtube-dl on the command line and have experimented with the "Import from YouTube" function on Peertube but ended up with a tiny cobbled-together video platform, importer (youtube-dl wrapper), and Firefox extension. I think the next step will be easily saving non-video things - probably recording WARCs?
I did that with only one YouTube playlist, so it wasn't too much work.