It should be saving the file you open to that folder, then. It needs a local copy in some capacity for you to edit it, and that’s where it should be at. Once you’re done editing, it should upload automatically. I should also note that I’m using the F-droid version of nextcloud on android, they did have to make changes to the play store version due to syncing policies from google messing things up.

I both open from nextcloud and from the folder. I did just check my settings, and I have two-way folder sync on the folder that I edit locally. Everything seems to update correctly if it was opened through nextcloud regardless of which folder it’s in, but only the folder I have sync setup on my phone updates if edited locally and only every 15 minutes. I’ll test some more things and check if something isn’t working as I expect. I did notice some settings had been changed and I wasn’t uploading from my phone as expected, so I have some confirmations to do on my end before I can absolutely confirm my phone is working properly.

As far as desktop goes though, I haven’t had any issues with it being unable to sync.