I’ll tell you what I use, appreciate that it doesn’t cover your needs (I was more focused on avoiding unskippable ads) and it’s a bit fiddly but it might provide a good starting point.

I also have a RPi 4 8Gb that runs a self-hosted Plex (Jellyfin would work even better arguably). “Playlists” are different Plex libraries.

For subscriptions, or channels where I want every vid, I have a crontab that wakes up once a week, downloads latest vids via yt-dlp, and puts them in the relevant Plex library.

For Discovery or ad-hoc vids, I rely on “real” youtube in my PC, and when I find something I want to watch I just manually share the link with a script in the Pi that will pull it via yt-dlp and put it in yet another “adhoc videos” Plex Library.

It works great for my purposes. A few caveats: There is the usual arms race between yt-dlp and The Formerly Not-Evil Company, so you need to keep updating yt-dlp every week or so. Also, the vids I like are transient, so I delete them after a month or so, but you can choose to archive them differently.

Don’t hesitate to reach out if you want more details, I can happily yap about it for hours :D