XCode (and hence most of the useful parts of using the Apple development ecosystem) as of v11.4 won't install on Macs running Mojave it's actually better, in my view, to use Mono/C# and things like Xamarin than start off with Swift and think you can port the other way and not be forced into upgrading your laptop for the privilege of writing apps for Apple systems.
It may be tempting to go the middleware route, but whenever I worked with middleware I had completely unrelated issues to the underlying framework which either complicated matters, or made it impossible to fix specific bugs. Then there’s the issue that Apple has a pretty aggressive release schedule. For a middleware maintainer it takes pretty long (compared to Apple’s native solutions) to adapt to these changes (I’m thinking about things like the notch on the iPhone X and safe areas). Apple’s secrecy about their upcoming release schedules doesn’t help, but it’s just how things are.
And just a minor nitpick, Apple’s development environment is called Xcode, where just the X is written uppercase.