Tbh fediverse is strange in that you use it for the decentralized federation model more than anything else.
Everything else is up to the instance and how it handles things.
Tbh people forget that open source just means that you can see the source code. It has no bearing on what you can do with it.
There are plenty of projects that are open source that have very restrictive licenses otherwise.
Just curious if you will eventually be able to post something from a Mastodon account to Lemmy or vice verse.
Or at least follow something on Lemmy from Mastodon.
Pretty sure you could do this by adding site blockers to your search query.