I don’t believe that they have very much proprietary code. I know that if you spin up their document server “community edition,” it has a limit of 20 simultaneous users without a support subscription.

This, however, can easily be legally patched around. It’s more just to make a point that it’s not supported without talking to them about a proper deployment. They also might have some code that is proprietary to make that large deployment easier, but it’s not required as long as you don’t mind the AGPL.

You can actually try this yourself with their NextCloud plugin. LibreOffice also has a cloud version available but it’s… let’s just say, in my opinion, it’s very bad.

You can open documents stored online in the desktop editors but there’s no offline syncing or anything so it effectively just opens a browser tab