Nanite not working: UE5 64 bit atomics not working, but working nicely in 4.27

Hallo, Nanite is not working here, win10, RTX3090, win driver and nvidia game drivers updated. Atomic 64 seems not working in UE5, but it is working in UE4.

UE5 Log:
LogD3D12RHI: AtomicInt64OnTypedResource is supported
LogD3D12RHI: AtomicInt64OnGroupShared is supported
LogD3D12RHI: AtomicInt64OnDescriptorHeapResource is supported
LogD3D12RHI: Shader Model 6.6 atomic64 is supported
LogD3D12RHI: Warning: Failed to query support for 64 bit atomics
LogD3D12RHI: RHI does not have support for 64 bit atomics

UE4 Log:
LogD3D12RHI: RHI has support for 64 bit atomics

Additionally: In Preview rendering level Shader model 6 is greyed out, although in Microsoft DirectX Capabilities Viewer my available shader model is 6.5…

There are no active plugins in UE5 except for Built -in ones.

Thank you for your help!