OSX - Disable Fullscreen Mode from the zoom button?
Here's what I figured out.
To change the behavior of the zoom button to normal window zooming (not by hiding the button), change the window to "Auxiliary" will do.
Attributes Inspector > Full Screen > Auxiliary Window
If there's a better answer to this, I'd be more than happy to accept that as the correct answer.
For SwiftUI:
.onReceive( NotificationCenter.default.publisher( for: NSApplication.willUpdateNotification), perform: { _ in for window in NSApplication.shared.windows { window.collectionBehavior = .fullScreenAuxiliary }})