I was in Rome about 3 weeks ago.
It was fabulous. Lots of tourists but mainly French and German (who drive down) Spanish and Americans, as it was just a couple of days before the 5 day quaratine for Brits ended. Definitely however, not as many tourists as there would usually be in August. So queues weren't so bad (for example it only took us about 10 minutes to get into Saint Peter's where we happened upon a cardinal's funeral which was cool (not for him I suppose!)
Obviously you need a Green Pass for lots of things: restaurants if you want to eat indoors, museums, intercity trains etc as pp says above. If you don't have a pass (if you have unvaccinated kids for example) it's really easy to get a quick LFT - there are pop up tents outside pharmacies and on street corners.
We booked in advance: Vatican Museum, Pantheon, Colosseum. Longest queue without a doubt was Pantheon (pre booking tickets doesn't give you priority entrance there)
Everything is very well organized and I felt very safe. Lots of security around as ever in a major capital city.
Mask wearing is obligatory inside and where SD can't be managed (around Trevi fountain for example) and it is enforced. Around the fountain for example we noticed the guards moving round reminding people to put their masks on correctly.