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2019 MacBook Pro w/ Radeon Pro 555X + 4K 120 Hz external monitor not working

  • Attempting to output 4K (3840 x 2160) at 120 Hz results in a blank screen.
  • 4K at 60 Hz works
  • Outputting a smaller, "low resolution" resolution less than 4K (e.g. 3360 x 1890) at 120 Hz works, but is obviously not ideal due to not matching the monitor's native resolution.
  • I've tried all four USB-C ports on the MBP


How can I get 4K + 120 Hz to work?


To get to the dialog below: option + click on "Scaled", enable "Show low resolution modes". Select resolution + refresh rate from the dropdown selector.



macOS 10.15.6 (19G2021)


MacBook Pro (15-inch, 2019)

2.4 GHz 8-Core Intel Core i9

32 GB 2400 MHz DDR4

Radeon Pro 555X 4 GB

Intel UHD Graphics 630 1536 MB


Monitor: Acer XB273K


Cable: USB C to DisplayPort Cable 8K 60Hz, Maxonar 6.6FT/2M (4K 60Hz 144Hz 120Hz 2K 240Hz) VESA Certified 32.4Gbps Type-C Thunderbolt 3 to DP 1.4 HBR3 Alt Mode Video Adapter for MacBook Pro/iPad Pro, XPS 15

https://www.amazon.com/gp/product/B08B3XNZGS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1




Posted on Sep 14, 2020 9:18 AM

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Question marked as Top-ranking reply

Posted on Sep 14, 2020 10:01 AM

Your Mac supports a maximum resolution up to 5120x2880 at 60 Hz at over a billion colors on up to two external displays or up to 4096x2304 resolution at 60 Hz at over a billion colors on up to four external displays via Thunderbolt 3 (USB-C).


Support for 4K @ 120 Hz is not listed.

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2019 MacBook Pro w/ Radeon Pro 555X + 4K 120 Hz external monitor not working

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