Anything similar for Windows and Linux?
For Windows there's a 5 year old blog post: https://www.swift.org/blog/swift-on-windows/
For Linux there's a guide for GNOME: https://www.swift.org/blog/adwaita-swift/
It would be really nice if instead we could just do one style of development and then ship a set of libraries as used to work for OpenSTEP (which was why it had "OPEN" in the name).
Swift on Windows has been part of the official distribution for a long time:
https://www.swift.org/install/windows/
The blog posts seems to place higher on search results --- maybe arrange to have it edited?
Which GUI toolkit(s) does that install support?
None, you’re on your own. The Browser Company made bindings for WinRT so you can use WinUI imperatively but it’s non trivial to set up.
I haven't shipped any Swift on Windows myself but I have a production Linux system using Swift (and C++ interop) and it works really well