I recently received a new Dell U2720Q 4K display to use with my 2020 13" Intel MacBook Pro. I planned to use the display at 2560x1440, basically the same res as on my old 27" but with better image quality.
When I attached the display with the included USB-C to USB-C cable, I was not able to get this resolution at 60 Hz, the max offered was 30 Hz which made mouse pointer movement jumpy. When I used a DP cable instead, the desired 60 Hz started working. The display supports DP 1.4 alt mode over USB-C as does my rather recent Mac. The USB-C cable I was using was the one included.
I would really like to use the display over USB-C since that way it will also charge my Mac. I don’t care about USB bandwidth downstream of the display because I’m not planning to use any USB devices attached to the screen. I did make sure to select the screen option to prioritize high resolution over data speed, which according to the manual should allow for 60 Hz up to 3840x2160. Any ideas how I can get this to work over USB-C?