> I wonder: Are there any Western apps which Chinese citizens would lose social credit or are officially prohibited from using?

That's not how it works. The apps are not officially banned, they are just unavailable or don't work. If they're not on the China iOS store (separate than US) then you can't install them, and if you went abroad and managed to install them, they just can't connect to the IG or whatever servers once you're back in China. Same for Android.