here is my standard checklist

* Color Depth (often default set to 16 bits or even 32 bits) need to be set to 8 bits (when running 4:4:4) or 12Bit when running in 4:2:2.

I am quite sure the adapter does not support higher color depth than 12bit.

* Make sure the HDMI port your using on the TV is HDMI 2.0 capable or 3840x2160p 60HZ capable.

Often TV’s have like 4 HDMI ports, but only 1 is suited for “2.0” standard.

* Make sure the HDMI cable you are using can do HDMI2.0 or 18Gbps.

* On many TV’s you need to turn on “UHD Color” manually in the settings of your TV for the HDMI port to which your pc is connected.

* Also it could help when connecting 2 screens, to set the screen connected thru the Adapter as second/secondary screen

* Try making a custom resolution and choose timing standard CVT-RB (reduced Blanking)