Update. I did this and sure enough the 4k 60hz modes appeared. Thanks again.
Hi I didn't enabled this option in config.txt and I was able to play 4k HEVC movie anyway. Is that possible? Now i tried enable this option and only difference is, that I can put Kodi interface to 4k 60fps mode, previously I could use just 4k 30fps.
I'm doing it right: I opened SD card on my computer, opened config.txt file and added line hdmi_enable_4k=1.
But i'm surprised, that 4k worked without this line.