Well FUCK that was a close one.

I was originally using the xmega32e5. Then I remembered the chip shortage.

Sure enough, almost impossible to find (real ones anyway). Same with the SVR I was planning to use.

Got lucky and had a bunch of attiny814s on had (and of course they are not out of stock anywhere), and it was easy enough to switch the code over. Also found another switching regulator that fit the bill and was simple enough not to need a prototype of the circuit.