On this WWDC '24 it will be 10th anniversary of Swift. Great milestone for language. There is so much work going on improving it. However From outside it does look like it still is few years away from being general purpose outside Apple ecosystem.
It's a shame, because Foundation.framework circa 1994 was a better standard library than any other language had at the time. Many have caught up since!
Swift has many virtues outside of SwiftUI -- real static typing, functional, sophisticated generics without all the gotchas of C++ templates, complete ABI, efficient exceptions, the syntax isn't so foreign to people used to C++/Java/Rust/Ruby/Python; I could go on and on.
I've written Objective-C code for 23ish years, and I like it a lot, but no one entering the workforce cares about its remaining virtues and the language has been mostly unchanged for almost two decades.
Also it’s a superset of C and C++ so you can mix all three in a single file, for better or worse.
But, in fairness, it’s a much simpler language than Swift. Which can also be a virtue.
Also Objective-C had comparably miniscule community effort in open source, the Swift on Server community is humming along, active, and businesses are using it on Linux. It's only grown in popularity... not sure Objective-C ever saw any amount of growth outside of Apple's platforms!
Secondly, yes Swift is quite relevant on Apple platforms, and that is exactly why the only ones that really care about using Swift on Linux, are mostly Apple shops writing the server side of their iDevice apps, since Apple killed OS X Server, leaving Linux distributions as the only option for server side.
This on Windows is kind of nice that it exists, but I doubt it will ever take off beyond what the folks at the Arc browser are doing.
The language is great, however the whole ecosystem speaks Apple Frameworks.