After some thinking, I came to the conclusion that it doesnt really make sense for Lemmy to accept only likes which are marked as public. I mainly implemented it that way because most other content in Lemmy is public, but in fact likes are expected to be private. This is a problem in federation with Friendica, which publicly lists all Lemmy users who liked a post. For that reason, i think it also makes sense to not mark Lemmy likes as public, meaning they will be private.
From nutomic in #2301:
This means that “favorites” from Mastodon or Pleroma should now count as votes on Lemmy. Havent tested it though.
I tested from Mastodon but votes seems not works
You can open an issue then.