Extremely High DNS Data Usage (GBs per Month)
Turns out my ad blocker (1Blocker) was the cause.  Once I disabled it, DNS usage flatlined to near zero.  I was chewing up 50-100MB a day in DNS and now it's been a single MB in a week.

Strangely, I have Safari blocked from using cellular.  I often tether another phone's hot spot for use, but that should burn data on that phone and not this one.  Still, 1Blocker burned a ton of data use on this phone.  I don't know if that means it's poorly designed or it was doing something shifty under the covers.