Merge conflicts on NextCloud are terrible, but for a KeePass file, I don't think this comes up very much. My laptop syncs from Nextcloud whenever it's online, and my phone syncs whenever it opens or modifies the file. Nobody else is using my laptop or phone, and certainly not my keepass vault. I would probably have to go out of my way to use both my laptop and my phone offline and add/change passwords during that time in order to get a merge conflict.