FWIW, you can sync files with Nextcloud on IOS and it works fine. Also automatically syncs photos which makes it a viable alternative for cloud storage on iPhone. What it doesn't sync are things like settings, though.
Did your photo's also recently got synced to JPEG (by NC), whereas at first the heic's were uploaded? Heic works poorly in browser on other platform so JPEG is ok, would prefer heic to work everywhere though...
