Can only 4K / 30Hz, can't 4K / 60Hz?

[lmjloavcj]

Can only 4K / 30Hz, can't 4K / 60Hz? Both type and HDMI lines have been tested. HDMI is sure to support 4K / 60Hz

[ccidral]

Unfortunately the Intel UHD 620 supports 4k over HDMI at 24Hz only. You'll have to use the DisplayPort over Thunderbolt which does support 4k at 60Hz.

I had the same problem this week when I got my 4k monitor. I had to use a USB-C to DisplayPort cable. Plus I also had to change the device properties in the config.plist file that's in the EFI partition according to WhateverGreen's Intel HD guide. Below is my device properties config. I used Hackintool to generate it.

		<key>Properties</key>
		<dict>
			<key>PciRoot(0x0)/Pci(0x1F,0x3)</key>
			<dict>
				<key>AAPL,slot-name</key>
				<string>Internal@0,31,3</string>
				<key>device_type</key>
				<string>Audio device</string>
				<key>hda-gfx</key>
				<string>onboard-2</string>
				<key>layout-id</key>
				<data>DwAAAA==</data>
				<key>model</key>
				<string>Sunrise Point-LP HD Audio</string>
			</dict>
			<key>PciRoot(0x0)/Pci(0x2,0x0)</key>
			<dict>
				<key>AAPL,ig-platform-id</key>
				<data>AAASWQ==</data>
				<key>AAPL,slot-name</key>
				<string>Internal@0,2,0</string>
				<key>device-id</key>
				<data>FlkAAA==</data>
				<key>device_type</key>
				<string>VGA compatible controller</string>
				<key>enable-hdmi-dividers-fix</key>
				<data>AQAAAA==</data>
				<key>hda-gfx</key>
				<string>onboard-1</string>
				<key>model</key>
				<string>Intel HD Graphics 620</string>
			</dict>
		</dict>

The recommended framebuffer (ie: 0x59120000) was the only one that worked for me. Mind you that while your external display is plugged your laptop's display to be disabled, which is not a problem for me. If you find a way to fix this, please let me know.