Hello I have Macbook pro 15 inch, 2017, I know it supports 4k/60Hz on external monitors. But when I connect it to the new Samsung UR55 28 inch 4k Monitor that also supports it, it gives only 30Hz normal resolution / 60Hz low resolution mode. Fix?

Hey ilia2020,

If we understand correctly, you are using an adapter and connected an external display and it is not providing the resolution you are expecting. You can try resetting the NVRAM and see if the resolution is available.

Are you able to try a different USB-C Digital AV Multiport Adapter?

"Video Support

Simultaneously supports full native resolution on the built-in display at millions of colors and:

• Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors

Thunderbolt 3 digital video output

• Native DisplayPort output over USB‑C

MacBook Pro (15-inch, 2017) - Technical Specifications

"This adapter allows you to mirror your Mac or iPad display to your HDMI-enabled TV or display.

3840x2160 at 60Hz on:

iPad Pro 11-inch, iPad Pro 12.9-inch (3rd generation and later), MacBook Pro (16-inch, 2019), MacBook Pro (15-inch, 2017 and later),"

USB-C Digital AV Multiport Adapter - Apple

Reset NVRAM or PRAM on your Mac

Please don't hesitate to let us know if you need additional assistance.

Thank you for using Apple Support Communities. Have a good one.