Since macOS Catalina: autosave fails on Dropbox vault (severe bug)

macOS 10.15.7
Cryptomator 1.6.6 (latest)
macFuse 4.2.4 (latest)

I upgraded to macOS Catalina last week. When opening and editing any text file (.txt) from my vault folder in Dropbox, it fails to autosave. See the screenshot. The only remedy is to discard the changes and duplicate the file or copy its contents into a new file.

This is annoying and clearly a Cryptomator-related issue. Who can help?

The autosave problem occurs irrespective of how the file is opened - whether by double-click in the Finder or through an app like Find Any File.

Under Cryptomator Preferences > Virtual Drive, I noticed that Volume Type was set to WebDAV and Fuse was not even an option. This is probably because Cryptomator was running at the time when I updated Fuse. So, I restarted Cryptomator and now Fuse has been recognized and it can be selected as volume type.

Now I am watching whether the autosave failure still occurs. If not, then I guess something about WebDAV was probably the cause for the autosave issue.