I’ve been trying to use iA Writer with NextCloud, but found that Nextcloud does not appear in the “Save To” screen with the other document providers. I tested again with the “Text Editor” app which supports both “Save To” and “Open From” and can see that Nextcloud is in the “Open From” list, but not in the “Save To” screen.
I’ve been in communication with the developer, and he is investigating, but it looks like a Nextcloud app issue instead.
It is a Nextcloud issue since it only supports read from at the moment, the write to part is something a contributor is working on from time to time.
Just checked, this is just discussed to some extent here: https://github.com/nextcloud/android/issues/303
I noticed this a few times too. Looking forward to seeing this get some attention.