I haven't tried it myself yet, but I self host my own Jellyfin(1) instance, and I've had it recommended to combine it with pinchflat(2), which will auto download and label entire youtube channels, as they publish new videos. So then you could use it to archive and provide access to the channels you want without worrying about the recommendations and other channels.
I have this workflow with the ytdl-sub docker on my k8 cluster, is pretty powerful at filtering to specific videos and includes sponsorblock - everything is configuration driven, no ui, which can just be dropped into a yaml configmap
I rarely have to touch it unless I'm adding a new playlist or channel
I've just started setting this up for my own family with plex instead of jellyfin, so I don't have a LOT of answers, but...
- yes pinchflat allows you to define the date at which it starts downloading. For a couple channels, I set it to only download the past year's worth of videos and it seems to have respected that properly. It also allows you to set a retention period
- it allows you to download, embed, and use autogenerated subtitles (three separate options)
1. https://jellyfin.org/
2. https://github.com/kieraneglin/pinchflat