Thanks! But no joy. I'm going to try Ubunutu Live next. I have reason to think it might work. I also welcome your further suggestions on the Debian front.
That's the short version. Here's the long version:
I downloaded /Users/kdeen/Downloads/buster-backports-10.3.1-amd64.hybrid.iso (your update). I copied it (dd) to USB stick.
I boot Mac while holding down option key. To my surprise, I see THREE boot options: (1) Macintosh HD, (2) EFI Boot, (3) EFI Boot. Both of the EFI Boots take me to a grub (I think it's grub) splash screen showing Build Time 2020-03-28 18:54:48. Beats me why "EFI Boot" appears 2x.
From the grub splash screen I hit Enter. I get a boatload of console messages scrolling by, many saying "[OK]". I did not notice any errors (progress). I land at a command prompt.
Keyboard fails, but failure mode now is different. I press any key, "a" for example, and instead seeing "a" echoed to the screen as I expect, I get a bunch of bluetooth error messages. (Huh? Bluetooth? I am not using Bluetooth!)
Here's why I'm going to try Ubuntu. If all of the statements below are true, then current Ubuntu versions 19.10 and 18.04.4LTS ought to work for me:
"Keyboard & Touchpad Works out of the box with Linux 5.3 and above for MacBookPro13,* and MacBookPro14,*." ( https://github.com/Dunedan/mbp-2016-lin ... --touchpad
"Ubuntu 19.10 includes a new Ubuntu kernel based on Linux 5.3 — and that kernel update will find its way in to Ubuntu 18.04 LTS via the Hardware Enablement Stack (HWE), due later this year. " ( https://www.omgubuntu.co.uk/2019/09/lin ... e-features
"If you downloaded Ubuntu 18.04.2 or newer desktop version, HWE is enabled for you and you’ll get the new kernel along with the regular updates by default." ( https://itsfoss.com/ubuntu-hwe-kernel/