Mac Mini M4 24GB and Dell DEU2724DE Monitor color contrast issues

What cable connection are you using between the Mac mini and Dell display...?

These new Mac mini's do not do well using cheap long poorly shielded video cables.

Test a short high speed 8K USB-C to DisplayPort 1.4 cable.

for example > https://www.amazon.com/dp/B09NVV76FH/ref=sspa_dk_detail_5?

Or optionally a short ultra high speed HDMI 2.1 cable.

for example > https://www.amazon.com/dp/B09HXPZ1PQ/ref=sspa_dk_detail_2?

for reference > Connect a display to Mac mini - Apple Support

It's all a matter of display calibration/adjustment. If you adjusted the display itself to get a good image from the PC, then it is quite likely those settings will not work with the Mac (or any other device) because you were using the display to correct for the PC's video card and drivers. You need to set the display at some nominal setting for brightness and turn off any "auto" features. Then use the computers to "calibrate/adjust" for proper viewing. Both Windows and Macs have tools in the OS to make these corrections and create profiles.

Go to Apple > System Settings > Accessibility > Display.

Turn off Increase contrast and set the Display contrast slider to Normal.

I've done what den.thed suggested but in the Dark Mode.

I also set the font size to no less than 28 points (not for this screenshot). It works beautifully for me.

You need choose the best Color Profile on the Mac mini side.

Then work with the Dell Displays Brightness and Contrast controls to get where you want.