No recent experience ( I think I took a HOHO bus in Rome long ago.) but have been to Rome some four times, spending in the range of 20+ days.
You can start here... https://www.rometoolkit.com/whattodo/rome_hop_on_tour_bus.htm they do a comparison, but my impression of the HOHO buses in Rome is while they circulate around the landmarks, they really do not get very close to them due to street patterns and pedestrian zones.
I really did not find them to be useful in Rome (I did in London, and in Paris they were nice for an overview), but with an injured foot? maybe.
I guess I would look at the linked article, then follow up with one or two companies and look at their maps. List where you plan to go, and using google maps, do a walking route to see how close you are and what the walk time would be. Try to find the location of the stop, realizing "Pantheon stop" may be blocks away from the Pantheon (it is not on the Piazza in front of the Pantheon).
You might also look into public transport, there were some routes done by small electric buses that went through the old center. Not sure with the pandemic if they are still running...even before they were on again/off again. The Metro line has expanded some as well, plus the regular bus routes and trams.