Should I add rel=sponsored to my affiliate links?
In short yes, John Mu from Google specifically said to use the rel=sponsored when possible in a Twitter post.
Yep. And definitely use rel=sponsored for affiliate links, if you can. And to be more complete: affiliate links are not bad. It's fine to monetize your site. Google's OK with that. There's no need to hide them, just use the right kind of link if you can.
He hinted that you won't get penalized, but it can help your SEO.