If you find you can't enable an extension in Safari, the fix is simple but ludicrous. I'm talking about the Safari Preferences -> Extensions tab where you can tick and untick extensions.
I disabled the 1Password Safari extension by unticking it and then it just wouldn't allow me to tick it again to enable it. I thought it was a 1Password-specific thing at first but then the same thing happened with Bear Writer's Safari extension.
Bizarrely, the way I fixed it was by simply moving the preferences dialog to the middle of the screen. I never noticed this before Safari 13.1 but it could feasibly have been there. I don't enable or disable extensions all that often and maybe when I have previously done so the dialog has been in the centre of the screen anyway.
It seems to me to be a very odd way to fix a problem and something weird must be going on there.