I should clarify: I didn't mean to say nothing[1], but it's certainly not common. The vast majority of server stuff at Apple is written in Java (which goes way back), with Go becoming more and more common and some Rust popping in around the lower level stuff. I'm sure there's some Swift in there somewhere but it wasn't anywhere I could see while I worked there.

Ironically, I was involved in the effort to port swift to linux so you'd think I'd know. The team I was on eventually moved most of our work to Rust (it was, also unusual for apple, written in C before).

[1] And anyone who would ever come into HN and tell you anything about what goes on inside apple could never tell you anything with that level of certainty because even in Services where things are generally more open, stuff is still very siloed and fragmented and no one has a complete picture of what's out there.