Re: This...
Downside of that is that, possibly to make way for it, NextCloud removed their Documents app in a point upgrade.
As far as I can make out the actual Collabora doesn't run under NC, NC just connects to it. Likewise, I suppose, the online LibreOffice. If that's the case these solutions aren't going to be available if you're running a personal NC instance on a Pi, as I'm doing, or considering running it on a hosted web service as I was thinking of doing.
The local Pi server isn't a problem - I just keep a desktop folder synced to the Pi. The idea of being able to economically run a hosted NC server to collaborate on a project with my local history group just hit the buffers if users have to download a file just to be able to view it - it doesn't offer enough advantage over an email list.