I have tried all 3 versions of nano (the chip is a 328) with the same result. The RX light gives a very faint (and almost imperceptible) blink.
To add to the mystery, I installed the Window's App version of the IDE from the Windows store and the board works fine. Same version (although this version, still 1.8.5, only has 328 and 168. No old bootloader) and same COM port selected. I can upload a code no problem. Hop right back to the other version and get the same error.
I can just use the app version, but I'd rather solve the mystery than just abandon the program. Especially in case the same thing goes wrong in the app version.