@ObservationIgnored weak var - must be initialised?

I understand that @Observable currently requires all properties to be initialised. However I am surprised that opting out of observation does not work:

@Observable class Assessment {
    var name = ""
    var processes: [Process] = []
}

@Observable class Process {
    var name = ""
    @ObservationIgnored weak var parent: Assessment?
}

The error message is Return from initializer without initializing all stored properties from the Process class. Any suggestions?