Solution: Using @Observable on a class that has a property that is a closure causes the Xcode beta 3/4 compiler to flip out. Using @ObservationIgnored on the said property will get the compiler to calm down.

update the Viewmodel code to this: @Observable class ViewModel { // MARK: - Navigation @ObservationIgnored var navigationPath: [Module] = [] @ObservationIgnored var titleText: String = "" @ObservationIgnored var isTitleFinished: Bool = false @ObservationIgnored var finalTitle: String = "Hello World" // MARK: - Globe @ObservationIgnored var isShowingGlobe: Bool = false @ObservationIgnored var globeEarth: EarthEntity.Configuration = .globeEarthDefault @ObservationIgnored var isGlobeRotating: Bool = false @ObservationIgnored var globeTilt: GlobeTilt = .none // MARK: - Orbit @ObservationIgnored var isShowingOrbit: Bool = false @ObservationIgnored var orbitEarth: EarthEntity.Configuration = .orbitEarthDefault @ObservationIgnored var orbitSatellite: SatelliteEntity.Configuration = .orbitSatelliteDefault @ObservationIgnored var orbitMoon: SatelliteEntity.Configuration = .orbitMoonDefault // MARK: - Solar System @ObservationIgnored var isShowingSolar: Bool = false @ObservationIgnored var solarEarth: EarthEntity.Configuration = .solarEarthDefault @ObservationIgnored var solarSatellite: SatelliteEntity.Configuration = .solarTelescopeDefault @ObservationIgnored var solarMoon: SatelliteEntity.Configuration = .solarMoonDefault @ObservationIgnored var solarSunDistance: Double = 700 @ObservationIgnored var solarSunPosition: SIMD3<Float> { [Float(solarSunDistance * sin(solarEarth.sunAngle.radians)), 0, Float(solarSunDistance * cos(solarEarth.sunAngle.radians))] } }