That nextcloud issue is quite weird and people seem to have had better luck with the sync app downloaded from places other than the Play store. I personally would lose any confidence in the app and use a completely separate thing to do the syncing if that happened to me. I actually did use the nextcloud client on pc a while ago and it was kind of fickle in other ways too anyway so I stopped using it.

I really like SeaFile for this kind of thing. It follows the "do one thing and do it well" philosophy. It's just file sync with some basic document editing features (markdown, .doc I think). Super fast and dependable, highly recommend.

https://www.seafile.com/en/home/