With private access tokens demo'ed at WWDC2022 [1] as a better replacement for captchas, this problem can be reduced to a great extent. As this becomes an IETF [2] standard that Google and Microsoft and many others will also implement, this will no-doubt be used to solve bots-in-ads problem.
1. https://developer.apple.com/videos/play/wwdc2022/10077/
2. https://www.ietf.org/archive/id/draft-private-access-tokens-...