Seafile uses some kind of non-standard storage format for the files IIRC, so that's a big downside.
If you want something simple and fast, check out a basic file browser that just works directly with files on the host like these:
https://github.com/filebrowser/filebrowser
If you need a mobile app vs just using the browser, you could spin up SFTPGo as a WebDAV server, since there are plenty of ways to connect to those from basically every OS.