I’m wondering this as well 5 years later. HackingWithSwift says it only works in a widget, but HolySwift infers it can work anywhere, but I cannot get it to work. https://www.hackingwithswift.com/quick-start/swiftui/when-should-you-use-containerrelativeshape https://holyswift.app/containerrelativeshape-swiftui-tutorial/

so how do we move windows around like desktop manager apps such as Magnet? https://magnet.crowdcafe.com/ They are in the mac app store, so how can they do this while sandboxed? I keep getting macOS AXError kAXErrorCannotComplete when I try to have my app manipulate other apps windows (I can successfully manage my own app windows)