Ads are supposedly based on what you watch and what they track you doing (total bullshit). I personally don’t allow yt to track me but it appears to be somewhat doing that anyways. It’s also influenced by what other people who watch your content also watch. If a lot of people with certain interests watch what you’re watching but you don’t have them, they’re still gonna give you ads for it.
Heres an example. I mainly use my YT account to listen to video game OST. Youtube for some reason gives me nearly full nsfw ads for f**king anime mobile games (no, I will not play your “boobtastic” game) combined with fake weight loss ads (“japanese pink salt trick” my ass) for the majority of them, I’ve rarely seen an actual normal ad. I had this flip flop back and forth for the majority of this summer and it’s just now starting to fix itself, though it’s being replaced by those weird right wing propaganda and christian church ads combined with military recruiters.
In contrast, when I don’t use my YT account, I see mostly normal ads with a few exceptions. I get some fast food chains, a few old spice ads here and there, but nothing too crazy except for the occasional bait mobile game ad.