Signal boosting Laura's post that you should absolutely download and archive the stuff that matters to you. The corporate internet is hostile to art and the things you love do not belong to you unless you claim them for yourself. If you've been around for a while on YouTube, just look at your "liked videos" playlist and see how many of the early ones are no longer available (something you literally have to enable in the playlist settings, it's that endemic).
The tools to do this in a basic way are extremely easy to get hold of, and generally have good defaults. I'm also going to talk a little about my own setup, and why it is the weird way it is, but it's definitely overkill for most setups. yt-dlp or one of it's many wrappers 1 will do most of what you need, and a folder on a bulk storage drive or NAS will be plenty sufficient to make sure you always have access to them.
