Rome bus , Uber or taxi. We’re staying at Numa Rome Barbarini

You can look on Google Maps for directions from your hotel to St. Peter's. Choose the public transit icon (looks like a train), and it will give you various bus options. Default is "depart now," so there may be fewer showing due to time difference.

We are in Rome and took taxis almost everywhere. We took the bus a bit but for 4 of us, the taxi was 9 euros most of the time and the bus was 6, so it’s not that much more and the buses were always crowded.

From the Numa go to via Veneto (half block) until you see the US Embassy in front of you. You can’t miss it. It has an American flag and it will have armored military vehicles and armed Italian soldiers in front. Turn left. At this point you have two choices. There is a taxi stand in front of the Westin Excelsior hotel (on the left side of the Embassy across the street) where you can take a taxi.
If you want a bus just walk a little further on via Veneto and there will be a bus stop (on the same side of the Westin). I don’t know if there have been changes to the routes, the the 590 bus will take you to near the Vatican Museum. The last stop is the Cipro metro station, which is 5 minutes from the museum.