Yes, there's no requirement to use Compose Multiplatform for UI with KMP. You can share Kotlin code at whatever level makes sense for your app.
There are apps that do this up to the presentation layer and bind native UI to shared viewmodels, including SwiftUI for iOS. I'm in the process of adding SwiftUI to a
sample app for my library now.
SKIE is super helpful creating improved Swift interop. I've got this
super basic example app that has SwiftUI calling shared Kotlin code.
Alternatively, you could just share repositories or other business logic elements. I've done this in other apps myself, with existing UIKit iOS and XML Android UIs.