As for Swift libraries, Stdlib is fully ported, Foundation can be spotty, the new Foundation-Essentials is small but growing. Swift-System has portable low-level path and such, and Shwift helps with fully async scripting.
As for supported platforms, Ubuntu seems robust, AWS is usable but marginal. Windows has some hurdles - technical, legal, and incentives - but VSCode support seems relatively good for non-GUI stuff outside windows API's.
Embedded has been landing in the main compiler and pushed by the Swift team lead. They're still issue-spotting, planning how (much) to live without a heap and the runtime metadata used for protocols, but the number of issues seems manageable for the intensity of effort, even though it's not Apple's priority.
With Swift 6.0, a breaking release, up next (in September?), it's likely embedded features could be both driven by the desire to make any breaking changes now, and blocked by other priorities.