I managed to find out the following:
• if I open UE5.1 with the -dx12 argument, a message appears that my system does not support DirectX 12.
• my system says DirectX 12 is supported. I can also run the DirectX12 benchmark in 3DMark.
• when opening UE4.27 with -dx12 it starts without any problems.
• UE5.1 allows “Track Markers” in “Meta Human Identity” even with DirectX 11 selected in RHI.
That’s why it worked in UE5.1 but can’t work in newer versions, looks like they removed DX11 support completely there. Btw the MetaHuman plugin is experimental.