Unfortunately, the AP63205WU (the buck converter to go from +12 to +5V) is out of stock everywhere and it appears like it won't be back in stock during 2022. Go figure.
I use this chip in a lot of things, it turns out, so I'm screwed.
In some cases, I can substitute an AP1509, but it's a SOIC-8 instead of a SOT23-6 and does not include a synchronous rectifier, so it means adding a Schottky diode to the circuit. There just isn't room for all of that on this board.
I'll post back when the 63205 becomes available again. But for now... I'm out.