Recently I purchased a 4K monitor for my Mac. I have a MiniDP to HDMI 2.0 converter and a HDMI 2.0 cable. I connected my late 2015 Retina iMac to the external monitor. I was able to get 4k@30hz on my external display. However, I was unable to achieve the 60hz refresh rate.
After some research I figured that late 2015 iMacs with the thunderbolt 2 ports should support 4k@60hz video output. I can't seem to figure out why I can't get the 60 Hz refresh rate.
When I open System Preferences, the
Refresh Rate drop-down menu is gray.
Mac Configuration: iMac (Retina 4K, 21.5-inch, Late 2015) MacOS: Catalina
I connected the same monitor to my 2018 MacBook Pro using a USB-C to HDMI 2.0 cable. My MacBook Pro was able to drive the display at 4k@60hz.
Thank you for your time and consideration!