I don't know if this is serious or not but I get zero ads with Youtube Premium even on my phone.

Youtube premium can look very different between places/people. Many with premium still see them. Youtube seems to be testing various markets to see how many ads it takes before people cancel their subscriptions. Also, you have to accept google cookies and such for them to identify you as a subscriber, so many privacy-focused users will see ads regardless of premium subscriptions.

I'd love more info about this, because I've been paying for Youtube premium for years and I haven't seen a single ad.

They have "premium lite" as an option for me (US) which says "most videos ad-free*"

what? I don't see ads unless the creator themselves are doing it, and even then it's two clicks on the right arrow button and we move on

Sponsorblock is a god send. It automates all that