I submitted feedback as FB16463501 -- posting here for others to see, or maybe for Apple to share any help if there are workarounds, etc.: Targets below iOS 18.x fail to launch app due to dyld[xxxxx]: Symbol not found: errors when referencing: MeshResource.init(from:) async - https://developer.apple.com/documentation/realitykit/meshresource/init(from:)-b7hb i.e. dyld[61511]: Symbol not found: _$s10RealityKit12MeshResourceC0A10FoundationE4fromACSayAD0C10DescriptorVG_tYaKcfC MeshResource.replace(with:) async - https://developer.apple.com/documentation/realitykit/meshresource/replace(with:)-8uvri i.e. dyld[78830]: Symbol not found: _$s10RealityKit12MeshResourceC0A10FoundationE7replace4withyAcDE8ContentsV_tYaKF Targets tested that exhibit issue: (DYLD errors) Device: iOS 17.7.2, iPhone 14 Pro Max Simulator: iOS 17.5 (21F79), iPhone 15 System Information: macOS Version 15.3 (Build 24D60) Xcode 16.2 (23507) (Build 16C5032a) MRE -- include this code in your app: (no need to invoke, just reference) static func addOrUpdateEntityModel_MRE(_ entity: ModelEntity) async { let descriptor = MeshDescriptor(name: "MyDescriptor") do { if let modelComponent = entity.model { // update existing ModelComponent if let model = try? MeshResource.Model(id: "MyModelId", descriptors: [descriptor]) { var contents = MeshResource.Contents() contents.models = .init([model]) try await modelComponent.mesh.replace(with: contents) /// `dyld[78830]: Symbol not found: _$s10RealityKit12MeshResourceC0A10FoundationE7replace4withyAcDE8ContentsV_tYaKF` } } else { //create new ModelComponent /// Comment-out the 2 lines below == dyld error for above `MeshResource.replace(with:)` let meshRes = try await MeshResource(from: [descriptor]) /// `dyld[61511]: Symbol not found: _$s10RealityKit12MeshResourceC0A10FoundationE4fromACSayAD0C10DescriptorVG_tYaKcfC` entity.model = .init(mesh: meshRes, materials: [SimpleMaterial()]) } } catch { fatalError() } }