"Powerpoint error saving file" when saving to Apache WebDAV

Question

I have my own WebDAV server using Apache2 on Debian 12. I connected it as a Network Drive in Windows and created a Powerpoint file on it. When I manipulate that file and try to save it afterwards, the mentioned error appears. Same behaviour with Word and Excel.

I suspected it could have to do with the temp files that MS Office creates (starting with tilde ~), so I enabled the dav_lock mod. No changes until now.

Any suggestions?