They should be mostly compatible. I used to use a Dell 27" monitor with my Mac Pro desktop, so I know it basically works. However---Dell is known to not play nicely with Macs of any species. I presume you are using an adapter to connect the Dell Monitor to your MacBook. I also presume you're not trying to get 4k out of the monitor--you just want a darn picture. Yes, check the adapter (if you're using one) and/or the cable. On the Dell, you should be able to switch and prioritize the inputs. See if the cable is HDMI 2.0 and HDCP 2.2 compliant.Under system preferences, then displays, go to scaled. choose either 30 or 60 hz, whatever resolution you can. Under "About this Mac" then "System report", the Dell should show up as a display. I don't know what OS you have on your MacBook, or the year, so can only give general suggestion. You might want to look for an EDID Override for Dell monitors on Mac OS X. That's what did the trick for me. Sometimes the monitor would be on, as in plugged in, and I could see the power light lit up, but no picture and no signal. Sometimes it would work, and sometimes not. The only way for me to fix it was to unplug the monitor's power cable frequently, wait about 30 seconds and plug it in again.
that's all I have
jb