I do have the option to create a SwiftUI project in the last version of xcode that would run on my OS, so it should support at least some of it. The question to ask, then, is how much of the new stuff, if any, this app uses.

edit: a lot of it. I tried changing the deployment target to 10.14 and building it. Got 101 "'SomeSwiftThing' is only available in macOS 10.15 or newer" errors.