So playing around with the Mehanik HDR test files which are 3840 x 2160 and HDR. The GB is set to output to 2160p and a HDFury Vertex2 gives the output specs from the GB.
I've noted that only 4K60 mp4 files are output from the GB at 4K. 4K24 mp4 files are output at 1920. The projector info confirms the resolution is 1920 rather than the mp4 files native 3840. Same with GB connected directly to Vertex" or pass through the AVR.
The all the TV signals are output at 4K50, irrespective of native resolution.
No doubt someone knows the reason??