Apple deploys a ton of their server stuff on Linux. Plus they appear to be doing all new code in Swift and moving old code over slowly.
They’re also using embedded Swift in the Secure Enclaves and other small processors due to its safety, though I think they have an extra layer of automated security checking that they use internally that doesn’t exist in the public builds.
But in short, yes. I believe they’re trying to use Swift for everything at this point and getting away from C/C++/whatever even for kernel work.
Most server code Apple writes is Java. They are slowly trying out Swift, but it's not really correct to say that all new code is Swift.
Yes their “private cloud” runs on Swift, which supposedly increases security because they believe Swift has things nailed by now.
The move to make swift run on Linux could be part of that work - their sysadmins, devops, and backend folks probably use Vim/VSCode and deploy on Linux.
We might see the release of a very good backend framework by apple for Swift that works on Mac/Linux.
The new macros they added kinda bolt on serde into the language too - and the distributed actor stuff is basically RPC in the language.