A Microsoft file hosting and synchronization service.
This is also happening on my iPhone 13 ProMax - for the record I have over 156GB of free space remaining on my phone.
Running IOS 17.3.1 with all other apps on the phone updated to the latest release.
I ran into the issue for the first time yesterday - been importing videos from the iOS app for months with zero issues
I rebooted the phone - no fix. Changed, removed and restored photo permissions - no fix.
I've reset OneDrive in settings, then uninstalled it, rebooted the phone - waited overnight - installed it again, logged back in, no fix - still won't save (went through the motions to download it again, but choked at the end and couldn't save).
Rebooted, tried again - won't even attempt to download it, just says can't save.
Videos are in .mp4, h.264 video/wav audio, tried 4 different videos from 38mb up to 276mb and none of them will save in the photo gallery.
I can see them in onedrive, I can see them in 0365 app as well (no option to download from there - should be added).