This app was mentioned in 3 comments, with an average of 1.33 upvotes
Google Maps does display ATAC bus info and other stuff too so I'm not sure why you aren't able to get it working, you need to press the bus icon instead of the walk icon. Anyways, the app I use is this and it displays live bus stop info about how much you have to wait and also does route planning.
Io uso Probus Roma, mi ci trovo bene e prende le informazioni direttamente dall'ATAC
https://play.google.com/store/apps/details?id=org.probusdev&hl=it
Aggiungerei SCOOTERINO, MOOVIT e PRO BUS