First let's get rid of the canard that the previous poster's Mac won't open Safari because she is using CleanMyMac.
I don't use it that app or any other on my late-2014 Mac Mini and exactly same result and error measure has appeared on my Mac.
Both the OS and Safari were modified when Safari upgraded to 12.6.5.
This is a stunning achievement by Apple!
Now my Safari does have an extension. It is the courtlistener Recap Pacer extension widely used by the legal, media and broader community to get preliminary partly complimentary access by Court Listener and other public open access legal sites.
I only use that on my latest iPad Safari (a) version anyway! Sure I would disable that if it's active but I can't launch Safari to do it.
So you can scratch that!
Next!