I have a 4k TV (Samsung 49NU7300) and a Windows laptop with Intel Core 8250U processor, connected with a 18GBps transfer speeded HDMI 2.0 cable, which supports 4k. According to the TV's and the Intel UHD Graphics 620's specifications, everything should be fine to set the refresh rate to 60Hz. The driver version is 18.104.22.16886 .
I have similar issue, I have Sony 65X850E , it works well with AMD R5 2400GE (with Vega 11) on 4K 60Hz even with DP to HDMI convert cable. however, same TV same cable if I'm using Intel i5 8500T (with UHD630) it only works on 4K 30HZ.
I'm still on the way to find answer...
I've did some research ( https://forums.tomsguide.com/threads/laptop-that-can-output-4k-60hz.422352/ , https://www.intel.com/content/www/us/en/support/articles/000023945/graphics-drivers.html ), and it should definitely support 4k@60Hz, with HDMI 2.0, and just 30Hz if the cable is 1.4 . Any suggestions?
Intel processors natively support DP 1.2 output (which is capable of supporting 4K@60Hz). A LSPcon chip is used to convert formats in order to support HDMI connectors. In order to support 4K@60Hz, this chip must have hardware- and firmware-level support for HDMI 2.0 and 4K@60Hz. I suggest you talk to your laptop vendor and see if they have provided a compliant chip. Note that it may take a firmware update to get support for this capability, so remember to ask them specifically about this.
Hope this helps,