We determined it was something fucked on the motherboard

So we sent the motherboard off to china for a replacement, took over a month

I get the new board back, I install it, and it works

Then it says "shut down and update"

Not having any other option, I let it run the update

The update was a BIOS update and it bricked the new board

So that's what killed his old board

No POST. Dead.

is there no way to manually flash the bios?

Not if it doesn't fucking POST

All I can do is find/make a dump of the SPI BIOS chip, which will carry over the serial and UUID

I do have a spare machine that's the same model but has a type C port

Fingers crossed it'll work