Is this the correct website https://www.tosc.it/en/artist/galleria-borghese/ for Borghese tickets? I can't get the other "official" website to load.
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, thatโs 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!