i experienced similar difficulties. what worked was to reshare my own old posts using the “double arrow”-icon, i think the servers see them as new content and sync it again (you can remove your repost afterwards, once it’s synced it stays visible.

setting the license type is only implemented on new posts, there isn’t any way to set them on existing posts, it’s probably on the roadmap with a low priority: https://github.com/pixelfed/pixelfed/issues/4525

When you start following and interacting with people on other instances, the federation kicks in and their content is slowly retrieved, but it can take a while depending on the load