I enabled undo using .modelContainer(for:, isUndoEnabled: true) and it worked fine. Cmd+Z etc on Mac, and shake to undo on iOS.
On adding the Mac Catalyst destination, undo no longer works. I thought this strange, so I created a new SwiftData project and, setup isUndoEnabled for the default app, and it really does disable undo after adding the Mac Catalyst destination.
Has anyone else experienced this, I can't find any info anywhere, but it seems odd that something this basic would break. Any workarounds?