CPU/GPU is Pentium Gold G5600 (Coffee Lake with Intel UHD 630 graphics).
Mainboard: ASUS H370-I (DP and HDMI 1.4 ports), Yamaha AV receiver connecter via DP port through Club 3D CAC-1070 DP to HDMI 2.0 adapter.
At 4K resolution refresh rate is limited to max. 30Hz only. On Windows using DP port and this P to HDMI adapter I'm getting 4K/60Hz even in 4:4:4 (RGB) mode with no issues.
I borrowed this adapter to a collegue that has Penttium G4560 (Kaby Lake with HD 610) - he's getting 4K/60Hz with LE 9 (unsure which build though).
So I guess this is driver limitation in LE 9 on UHD graphics ?