Restore Window Size on MacCatalyst Apps

Sometimes its easier to just enable MacCatalyst on an iOS app to bring it to the Mac than to fiddle around with a dedicated Mac target or using the Mac version of SwiftUI. The drawback is that you don’t have access to AppKit but have to stick with UIKit / SwiftUI. So some quite useful features of AppKit are not available in MacCatalyst.

E.g. there is this nice AppKit construct to save and restore the window size and position between app launches:

But there is no equivalent in MacCatalyst since iOS apps don’t mess around with windows. In this post I’ll show how to achieve a similar behaviour in MacCatalyst.