libaws-checksums.dylib.PLATFORM_MAC_ENABLE_EXPERIMENTAL_NANITE_SUPPORT=1 in UEBuildMac.cs (Engine/Source/Programs/UnrealBuildTool/Platform/Mac/UEBuildMac.cs). UE_EXPERIMENTAL_MAC_NANITE_SUPPORT in spirv_msl.hpp.UEBuildMac.cs.bSupportsNanite=true and bSupportsUInt64ImageAtomics=true in Data Driven PlatformInfo.ini (Engine/Config/Mac/DataDrivenPlatformInfo.ini).