Edited the my post but it is currently mac mini usb-c male to DP male and macbook pro retina 15" 4 port (2017?) via usb-c male to usb-c male 3ft DP-alt (comes with this cable). There's 3 inputs on the Dell Q2720U. I think I bought the Belkin usb-c DP cable. I was using HDMI 4k certified monoprice cable (2 pack which I also use with my older non-4K tv) but ran into the "No Signal" issue every week or so. I do pretty much live on one electronic device or another, though, so prob. boot up the mac mini every day. Yes, I still shutdown my devices which probably shows my age.

I'll need to check the resolution each system is set at tomorrow. It's set pretty close to the same resolution at 60Hz on both machines but honestly, it seems to drop down into 30Hz at times (con of restarting systems, I guess). It may need more than 16GB memory without eGPU to watch YouTube 720p or 1080p in a full window. Will double check when I lookup the resolution settings.

I don't feel Mac Mini fan temperature management is as good as the iMac and would probably get a quiet 200mm usb powered fan like Noctua or AC Infinity if my area wasn't headed towards mostly cooler weather though similar caveats also apply to the MBP 15". Overall, I don't feel it is as nice of machine as the non-retina iMac, a little more iffy, but also the less expensive option if you want to connect more than one machine via hardware to a single display on your desk and near term if you want an Intel processor. The more expensive one would be a MB laptop or Mac Pro.