New iPhone 12 Pro Max. Set it up as a new phone (my yearly purge), and lo and behold, the non-notification iMessage started immediately. I had just wiped my 11 Pro Max to return to AT&T as part of my Next plan. I did not experience the same problems on the 11 Pro Max, for the week or so that I had been using both phones (11 Pro Max was running iOS 14.2 too).
I could not figure why I wasn't receiving notifications all day, especially on a weekend. I tinkered around with the usual suggestions, and was beginning to get really frustrated, after all I had just spent two days going through every app from my old phone (I use iMazing software for my physical backups).
Anyway, after growing increasing ****** off (c'mon these are $1400 phones), I found this thread and decide instead of wasting anymore time, and taking into consideration that I haven't used iTunes in years, I'd go the iTunes "iPhone Restore" + "Restore Backup" route.
And it worked. And it actually didn't take all that long.
Get it together