Borghese gallery tickets

Yep, that's the one!

That 'other' official one (https://galleriaborghese.beniculturali.it) is one of those wonky Italian attraction sites that's only active during the hours that attraction is open BUT their ticketing vendor is 'up' 24/7. The Colosseum has one of those wonky websites too.

You can also search in the forum, I forgot which site we used, but we bought tickets from the official site based on something we found in an old post on this form. And by the way you get a two hour window to be there, that’s different from the last time I was in Rome.

https://www.tosc.it/en/artist/galleria-borghese/ ( linked by the OP above) IS the official ticketing site.

Back in September we successfully used www.tosc.it. Fabulous collection!

And by the way you get a two hour window to be there, that’s different
from the last time I was in Rome.

That means you are assigned a time slot, and you have two hours to complete your visit. The museum is not large so it's entirely possible to do that, especially if being a bit selective about how long/short to linger over individual works. You need to arrive a minimum of 1/2 hour before your assigned slot to check items at the cloakroom which are not allowed in the galleries, use the restroom, etc.

The 2-hour time limit has been in effect for at least the last 20 years, if not longer.