Forget the official phone client and use FolderSync. It integrates perfectly (and seamlessly) to the nextcloud dav endpoint and you have way more options to fin

Forget the official phone client and use FolderSync. It integrates perfectly (and seamlessly) to the nextcloud dav endpoint and you have way more options to fine-tune how and when and what you want to upload. There are so many bugs in the phone clients, I ditched it two years ago, since then I'm super happy with the whole thing!