The HDMI connection is in place of oldest RPI with LibreElec which had no connection problem.
My GT King is connected via HDMI to Denon AVRX2500H which is connected via HDMI to a recent TV Samsung UE75MU7005
4K movies where read correctly before I change SDR to HDR option.
Actually the problem is not with 10BIT HDR x265 4K files (demo files) but with 8_bit SDR x265 4K files
demo files seems to have not this problem. They only stop to commut to HDR (I suppose) like before, but movie can be read. No black screen and wonderful colors !.