One doesn't need to use SwiftUI for the look. Things like the tab bar, navigation bar are available in Swift too. (for those unfamiliar, Swift is different and older than SwiftUI).
Surely you mean UIKit, not Swift? Swift is indeed older than SwiftUI, but is a language, not a UI framework, and there are no “things like tab bar, navigation bar” available in Swift per se: a framework gotta be used.