My take on the propagation of anchor preferences. Inspired by @Pyroh (https://github.com/Dimillian/ACHNBrowserUI/commit/133d3a3b8cb72d163ea58e6e1fed017a8c97c536)

View+propagate.swift

import SwiftUI

extension View {
    func propagate<Key>(
        _ transform: @escaping (CGRect) -> Key.Value,
        of source: Anchor<CGRect>.Source = .bounds,
        using key: Key.Type
    ) -> some View where Key: PreferenceKey {
        _propagate(transform, of: source, using: key)
    }
    
    func propagate<Key>(
        _ transform: @escaping (CGPoint) -> Key.Value,
        of source: Anchor<CGPoint>.Source = .center,
        using key: Key.Type
    ) -> some View where Key: PreferenceKey {
        _propagate(transform, of: source, using: key)
    }
    
    private func _propagate<Key, AnchorValue>(
        _ transform: @escaping (AnchorValue) -> Key.Value,
        of source: Anchor<AnchorValue>.Source,
        using key: Key.Type
    ) -> some View where Key: PreferenceKey {
        overlay(
            GeometryReader { proxy in
                Color.clear
                    .anchorPreference(key: key, value: source) { transform(proxy[$0]) }
            }
        )
    }
}

View+store.swift

import SwiftUI

extension View {
    func storeValue<Key>(
        from key: Key.Type = Key.self,
        in storage: Binding<Key.Value>
    ) -> some View where Key: PreferenceKey, Key.Value: Equatable {
        onPreferenceChange(key, perform: { storage.wrappedValue = $0 })
    }
}