With FEP-c118 there is currently an extension to the activitypub protocol in the works to allow setting a license on posts. If you don't add a license info in your posts the licensing is unclear. I think that some jurisdictions give a default copyright and some protections to the author but I don't know how that works.

With the fediverse you you have as much or as little rights as when you put it on your private blog without explicit licensing. If someone uses your works without your consent you still have to find out and you have to protected your rights yourself.

There are currently no lemmy or kbin instances that have monetization options. The only ActivityPub software I know that can show ads is misskey.

In the end you have to be aware that any kind of open social network is like screaming your thoughts towards a big crowd. You lose most of your control over it the second it's out. It is nearly impossible to track who has the information and who shares it with others.

There are legal protections in some parts of the world but even then you first have to find out that something bad happened. If an instance were to start monetizing data it would probably cut off pretty fast and all the communities would probably move.

Still if there is stuff you don't want everyone to know don't post it publicly.