Xcode 26/16.4 Metal Toolchain generates metallib's that are not compatible with iOS 16

Below is the error output from FirstPerson template as a C++ project:

{+}../../../FirstPerson58CPP/Content/firstperson58cpp_sf_metal_es3_1_ios-metal_es3_1_ios.0.metallib, 5881486 bytes!
2025-09-23 17:43:18.945898-0400 FirstPerson58CPP-IOS-Debug[13763:226460648] serializedRequest, line 411: error 'Corrupted library'
serializedRequest:411: failed assertion `Corrupted library'
2025-09-23 17:43:18.946233-0400 FirstPerson58CPP-IOS-Debug[13763:226460649] serializedRequest, line 411: error 'Corrupted library'
{{}}

which eventually leads to a crash at PSO creation time.

#21    0x000000010da3976c in NS::Object::sendMessage<MTL::RenderPipelineState*, MTL::RenderPipelineDescriptor const*, unsigned long, MTL::RenderPipelineReflection* const*, NS::Error**> [inlined] at /Users/<username>/Perforce/UE5Main/Engine/Source/ThirdParty/MetalCPP/Foundation/NSObject.hpp:216
#22    0x000000010da3974c in MTL::Device::newRenderPipelineState [inlined] at /Users/<username>/Perforce/UE5Main/Engine/Source/ThirdParty/MetalCPP/Metal/MTLDevice.hpp:1039
#23    0x000000010da39718 in CreateMTLRenderPipeline at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Apple/MetalRHI/Private/MetalPipeline.cpp:1061
#24    0x000000010da2da84 in FMetalShaderPipelineCache::GetRenderPipeline at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Apple/MetalRHI/Private/MetalPipeline.cpp:281
#25    0x000000010da2ab68 in GetMTLRenderPipeline at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Apple/MetalRHI/Private/MetalPipeline.cpp:1286
#26    0x000000010da277e8 in FMetalGraphicsPipelineState::Compile at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Apple/MetalRHI/Private/MetalGraphicsPipelineState.cpp:39
#27    0x000000010da27600 in FMetalDynamicRHI::RHICreateGraphicsPipelineState at /Users/stephane.jacoby/Perforce/UE5Main/Engine/Source/Runtime/Apple/MetalRHI/Private/MetalDynamicRHI.cpp:82
#28    0x000000010479bb98 in RHICreateGraphicsPipelineState at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/RHI/Public/DynamicRHI.h:1187
#29    0x000000010479d4c0 in FCompileGraphicsPipelineStateTask::CompilePSOInternal at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/RHI/Private/PipelineStateCache.cpp:3377
#30    0x000000010479d154 in TCompilePipelineStateTaskBase<FCompileGraphicsPipelineStateTask, FGraphicsPipelineStateInitializer>::CompilePSO at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/RHI/Private/PipelineStateCache.cpp:3217
#31    0x000000010479e1cc in void InternalAsyncCompilePipelineState<FCompileGraphicsPipelineStateTask, FGraphicsPipelineStateInitializer>(FGraphicsPipelineStateInitializer const&, EPSOPrecacheResult, bool, FPipelineStateAsync*, FPSOCompilationDebugData const&, bool)::'lambda'(FPSOPrecacheAsyncTask const*)::operator()(FPSOPrecacheAsyncTask const*) const at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/RHI/Private/PipelineStateCache.cpp:3656
#32    0x000000010479e178 in Invoke<void InternalAsyncCompilePipelineState<FCompileGraphicsPipelineStateTask, FGraphicsPipelineStateInitializer>(FGraphicsPipelineStateInitializer const&, EPSOPrecacheResult, bool, FPipelineStateAsync*, FPSOCompilationDebugData const&, bool)::'lambda'(FPSOPrecacheAsyncTask const*)&, FPSOPrecacheAsyncTask const*> at /Users/stephane.jacoby/Perforce/UE5Main/Engine/Source/Runtime/Core/Public/Templates/Invoke.h:47
#33    0x000000010479defc in UE::Core::Private::Function::TFunctionRefCaller<void InternalAsyncCompilePipelineState<FCompileGraphicsPipelineStateTask, FGraphicsPipelineStateInitializer>(FGraphicsPipelineStateInitializer const&, EPSOPrecacheResult, bool, FPipelineStateAsync*, FPSOCompilationDebugData const&, bool)::'lambda'(FPSOPrecacheAsyncTask const*), void, FPSOPrecacheAsyncTask const*>::Call at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Core/Public/Templates/Function.h:292
#34    0x000000010479aac0 in UE::Core::Private::Function::TFunctionRefBase<UE::Core::Private::Function::TFunctionStorage<true>, void (FPSOPrecacheAsyncTask const*)>::operator() at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Core/Public/Templates/Function.h:414
#35    0x000000010479a754 in FPSOPrecacheAsyncTask::DoTaskWork at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/RHI/Private/PipelineStateCache.cpp:690
#36    0x0000000103312034 in FAsyncTaskBase::DoWork at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Core/Public/Async/AsyncWork.h:288
#37    0x00000001033141f0 in FAsyncTaskBase::DoThreadedWork at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Core/Public/Async/AsyncWork.h:312
#38    0x00000001033fd168 in FQueuedThread::Run at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Core/Private/HAL/ThreadingBase.cpp:1469
#39    0x00000001033f7810 in FRunnableThreadPThread::Run at /Users/s<username>/Perforce/UE5Main/Engine/Source/Runtime/Core/Private/HAL/PThreadRunnableThread.cpp:25
#40    0x000000010331b9c0 in FRunnableThreadPThread::_ThreadProc at /Users/<username>/Perforce/UE5Main/Engine/Source/Runtime/Core/Private/HAL/PThreadRunnableThread.h:187

This is likely a bug in Apple's Metal Toolchain and should be discussed with Apple.

Run any template on an iOs 16 devices building against Xcode 16.4, 26.0 or 26.0.1.