OpenSource means you may look into the algorithms that decide what you see and everything technical. You may find for example that Lemmy doesn’t use an algorithm that is trained to make you addicted.

The fact that likes are basically public is a byproduct of the federated aspect of Lemmy and somewhat also a design choice. (Since otherwise it would be hard to make your upvote count on all federated servers)

Use bookmarks and only your server admins have insight into what you like. Use offline bookmarks and the data is yours. (Or selfhost)