[noggin]

ops! I already formatted sd card and downloaded nigthly did I mess up everything ? So if I understand you correctly tomorrow I need to try it with another hdmi cable, no need to try editing ini file ?

You needs to use a 18Gbps capable HDMI cable once you move into the 4K/ 60p HDR realm.
I use the cheap 18Gbps Amazon basics ones, about 2 meters in length.

Those cables are even good enough for the Ultra demanding, and very picky 4K DolbyVision streaming from my Apple TV 4K.

PS if you have a decent 4K HDR TV that has great picture upscaling, run CoreELEC Kodi at 1080p and let the 4K TV upscale all non 4K content (including the 1080p Kodi user interface).

CE Kodi will auto Resolution switch to 4K when viewing 4K content anyway.  

I don't understand, how it can be about to using a 18Gbps capable HDMI cable once I move into the 4K/ 60p HDR realm? It's just boot screen and I don't think it's 4k or high bit rate video, and if it was about hdmi cable then I mustn't see coreelec logo on my TV 2 times after I turn on N2, after that logo shown I guess N2 try to send video signal in wrong resolation or something else. But anyway I will try a quality hdmi cable tomorrow.  

I think the Core Elec boot screen is 1080p - but if you have a 4K display, the N2 will switch to 4K60 when Kodi itself starts running (as your TV will tell your N2 that it supports 2160p60 modes).  

This means that you get the boot screen but may not get the Kodi screen if your HDMI cable can't reliably carry the higher bandwidth HDMI 2.0 modes required for 2160p60.  

When I upgraded to a UHD TV, UHD capable AVR, UHD Blu-ray player, Apple TV 4K etc. I had to replace pretty much every HDMI cable in my installation as they all had issues with 2160p60 4:2:2 video - and either gave me drop outs, sparkles, unreliable connections or 'Unrecognised format' type errors.

I DIDN'T pay for expensive 18Gbps cables - but did ensure the ones I purchased were low cost, good value, HDMI Premium Certified with an official hologram logo on the packaging.