"Safari detected that an app or service interfered with clicking" ("Safari ha detectado que una app o servicio ha interferido con el clic")
Recently I had a problem with macOS Catalina 10.15.6 that Safari did prevent enable extensions. After many retries, and browsing the Internet forums, I decided to try another way. And I finally found the solution:
With a text editor, for example, nano, edit the file Extensions.plist (ensure Safari is closed):
$ nano ~/Library/Containers/com.apple.Safari/Data/Library/Safari/AppExtensions/Extensions.plist