My M1 mini was YPbPr on my U2520D for the last 3 days, and today I used HDMI cable to test if it looks better - it didn't. I unplugged it and replugged USB-C cable and now it shows RGB I don't know how it happened but it works perfectly..
I restarted several times both mini and display - so I'm assuming there might be a connection there. At least in my case. Because I haven't done anything else.
I'm considering the U2520D, is it working on RGB now? Also, what HDR setting did you use on the Dell OSD/MacOS display settings, and how is the sharpness of text like? Thank you.