How to fix the email Signature button not working in Outlook 2016 on Windows 10
Uninstalling desktop apps
1. Firstly click on the Windows button then on the Settings button that looks like a cog.
2. Next Click on Apps and Features and look for Desktop apps.
3. Now Click on Desktop Apps and click on Uninstall.
4. Open and close Outlook and you should be able to click on the Signature button.
