CustomScrollTarget.swift

import SwiftUI

struct CustomScrollTargetBehavior: ScrollTargetBehavior {

    func properties(context: PropertiesContext) -> Properties {
        var properties = ScrollTargetBehaviorProperties.init()
        properties.limitsScrolls = false
        return properties
    }
    
    func updateTarget(_ target: inout ScrollTarget, context: TargetContext) {
        // Temporary value
        let componentRect = CGRect(x: 0, y: 0, width: 200, height: 400)

        let targetMinY = target.rect.minY
        let snapY = targetMinY <= componentRect.midY
            ? componentRect.minY
            : componentRect.maxY

        if componentRect.minY <= targetMinY, targetMinY <= componentRect.maxY {
            target.rect.origin.y = snapY
        }
    }
}

#Preview {
    NavigationStack {
        ScrollView {
            LazyVStack {
                Color.yellow
                    .frame(height: 400)
                ForEach(0..<100) { index in
                    Text("Item \(index)")
                        .padding(.vertical)
                        .frame(maxWidth: .infinity)
                }
            }
        }
        .scrollTargetBehavior(CustomScrollTargetBehavior())
        .navigationTitle("Custom Scroll Target")
        .navigationBarTitleDisplayMode(.inline)
    }
}