DependencyBag.swift

import Foundation
import SwiftUI

public struct DependencyBag<Dependency, Content: View> : View {
    public init(
        dependencyFactory: @escaping () -> Dependency, 
        @ViewBuilder view contentFactory: @escaping (Dependency) -> Content
    ) {
        self.dependencyFactory = dependencyFactory
        self.contentFactory = contentFactory
    }
    
    @State fileprivate var bag = Bag<Dependency>()
    
    private let dependencyFactory: () -> Dependency
    private let contentFactory: (Dependency) -> Content
    
    public var body: some View {
        contentFactory(bag.getOrMake(using: dependencyFactory))
    }
}

private final class Bag<Dependency> {
    
    private var dependency: Dependency?
    
    func getOrMake(using factory: () -> Dependency) -> Dependency {
        if let dependency {
            return dependency
        } else {
            dependency = factory()
            return dependency!
        }
    }
}

Example:

struct ItemList: View {

    @ObservedObject viewModel: ItemListViewModel

    var body: some View {
        List(items) { item in 
            NavigationLink {
                DependencyBag {
                    ItemDetailViewModel(item: item, api: viewModel.api)
                } view: { viewModel in 
                    ItemDetailView(viewModel: viewModel)
                }
            } label: {
                Text(item.title)
            }
        }
    }
}

struct ItemDetailView: View {

    @ObservedObject viewModel: ItemDetailViewModel

    var body: some View {
        // ...
    }
}

final class ItemDetailViewModel: ObservableObject {
    let item: Item
    let api: APIClient

    init(item: Item, api: APIClient) {
        self.item = item
        self.api = api
    }

    // ...
}