Signatures and some other buttons in Outlook 2019 (Office 365) Mail Options are not working. Pressing a button either does nothing or Outlook hangs for 30-60 seconds.
The issue was caused by some MS Office related modern apps that came preinstalled on the computer (DELL OptiPlex). After removing "Microsoft Office Dekstop Apps" and "Office" the issue went away.
Microsoft Office 2019
Microsoft Office 365
Windows 10 Pro