I am very new to linux and all the open source stuff (my first post on lemmy actually) so I don't get how this stuff works but flathub is saying that floorp is proprietary. But after a quick google search it says that floorp is open source licensed under MPL 2.0
You can view and contribute, so do all the help possible but you can't modify/rebuild/release a different version. That is not open source, that is called open to volunteer.