'New' Catalina Install on MBP: Safari does nothing

Hi,

I'm finally at the tail end of a nightmare with my friend's 13" MacBook Pro. I'll spare you the details...

He had upgraded to Catalina, but because of incredibly poor performance (and it 'breaking' Microsoft Office) I tried to downgrade him to High Sierra. Long story, short...that wasn't successful either so now I've put his system back on Catalina. (He'll be using OpenOffice as his MS replacement.)

I've got a few minor issues that will simply have to be accepted, nothing major. But...the one issue I'd like to remedy is with Safari. It does nothing.

Safari will launch, it runs. But it won't reveal a window other than its preference panel. It will not open webpages, no new windows, no tabs, nothing.

I'm already so exhausted by this entire fiasco that my energy is pretty much gone. I'd like to get this last hurdle dealt with, but in reality, my friend mainly uses Firefox for browsing anyway. So if Safari ends up being DOA, then he'll just have to work around it.

If the 'fix' is going to be another attempt at reinstalling the OS, I probably won't have the stamina for it at this point. I'd like to fix this problem but it won't be the end of the world if this is how it's going to be moving forward.

FWIW, the machine is a mid-2012 13" MacBook Pro (retina) running 10.15.7 and Safari 13.1.3.

Thanks!