It's open source but only because in this way they can use GPL 3 libraries. The repositories have missing resources and you can't compile it by yourself.

Not that I wanted to waste a whole week trying to compile an office suite, but for example I wanted to fix a translation, and that's not public. You have to contact them by email and suggest the translation fixes as the language translation repository is only under NDA

This said, better than nothing, and at least they don't try to pretend they're as open as LibreOffice. On their website they're targeting enterprises and being open source it's a side note.

They're not like Proton where they boast being fully open source, sponsoring articles on itsfoss, but then the most important part, the server, is secret and proprietary and anyway good luck understanding how to compile the client from a giant all-in-one repo with no documentation