We are sorry for the trouble. As described you are unable to unable to login to sharepoint and getting the grey login prompt.
Would you mind sharing the version of the Adobe Acrobat DC and the Mac OS you are using? To check the version of the application go to Help > About Adobe Acrobat and make sure you have the latest version 20.12.20043 installed. Go to Help > Check for Updates.
Please try to add a different location (OneDrive, Dropbox, etc) and check if they are working fine.
If it still doesn't work , please try to create a new test user profile with full admin rights or enable the root account and try using the application there and check.