Through some trial and error (about 6 hours worth) and reading a lot of helpful hints from the community, I disconnected the HDMI to HDMI cable, and left in place the USB-C to USB-C cable that came with the monitor. The Mac Mini recognized the monitor while the monitor searched for it's connection. The Mac Mini's desktop appeared.
I logged in to the computer,
connected to the internet,
installed antivirus software,
successfully downloaded and installed a DELL firmware update,
and tested the webcam.
I set up a Zoom meeting, and the webcam was awesome. Sound was very soft, even though I raised the volume on the Mac as high as it would go. The volume control of the monitor didn't respond.
I turned everything off and came back later. This time I could adjust the volume control, so I'll test it all out with another Zoom meeting today. I think I'll be all set.