MS WORD won't save AutoRecovery files.

(Mac OS Big Sur 11.0.1; MS WORD 15.25) As soon as the Autorecovery tries to save such a file (5 min. after opening it) I get the message "word is unable to save the autorecover file to the location you specified etc."

I have checked that this location is correctly defined in Word's preferences (and changed it a few times to make sure that's not the problem), also that I have the permission to write to that directory. I also discovered that it DOES create an autorecovery file for a very old file I have, but not for new files.

(Rather frustrated having lost two days' work yesterday).

Any ideas?

(I followed replies to when a similar problem was raised in this forum years ago, to no avail)