The issue is the stuff I post being monetized by Zuck et al. I'm not interested in providing free content for billionaires.

If I understand correctly, the concern is not for the users on Meta's "Threads". It's the fact that the content you create on Mastodon or whatever fediverse part with which Meta federated would eventually reach users on Threads, and thus "you" (on the fediverse corner outside of Meta) are indirectly monetized.