Bug fix: Safari 13 Extensions will not enable

Safari extensions will not enable in the Safari / Preferences / Extensions pane - i.e. I have loaded the latest Extensions from the App Store and when you click on the tick box, the box will not tick enabling the Extension.

Set-up:

• Late 2016 MBP with Catalina 10.15.3 and using Safari 13.0.5 - both the latest version available as far as I am aware.
• Safari Extensions installed:
  • 1Password
  • Evernote Web Clipper and
  • Bitdefender Antivirus for Mac
• I have the latest version of these Apps and their Extensions.
• In Safari:
  • Safari Develop menu switch on.
  • Within the Develop menu:
    • Disable Extensions is not checked
    • Allow unsigned extensions is checked
  • Using the Develop menu I have Empt(ied) Caches.

Checks I have made:

• Ran Etrecheck - no issues to resolve or resolved
• Tried to find and delete the com.apple.safari.plist - cannot find that prefs file in the Library - which I find strange.
• Restarted my MBP in Safe Mode
  • Tried to enable the extensions - still did not work.
  • Tried to Disable Extensions, restart Safari and unchecked Disable Extensions - does not work.
• Restarted back into Normal mode:
  • Tried again to enable Safari extensions - does not work
• Reinstalled Catalina
  • Launched Safari
    • Tried to enable Extensions - still does not work.

I posted this message requesting some bug fixing help!