THIS IS THE SOLUTION FOR THIS ANNOYING ERROR!!! Thanks a lot!
I was searching for ages... All old solutions won't work. My folder was empty. No file like "linkCreation.dotm" and "SaveAsAdobePDF.ppam" was there.
Use the Library folder and NOT the User/Library/
--> Macintosh HD/Library/Application Support/Microsoft/Office 365/User Content/Startup
Both files are now in there.
Afterwards you will be getting an error when opening Powerpoint, but now you're able to go to Add-ins and remove the Adobe Add-in via "-". This was not possible before and unselecting always activated it again on startup.