Since I can’t work because I’m waiting for the replacement, I started tinkering to see what I could do and it turns out that the T2 security chip was totally nuked – the weird version of iOS it runs (BridgeOS) was broken/missing, which means the hardware won’t even power on, POST, or light up the screen to tell you. Without the T2, you don’t have a computer anymore, basically.
Turns out that this chip can be flashed by using a specific set of incantations: https://support.apple.com/en-ca/guide/apple-configurator-2/a...
So, here’s what I had to do:
1. You need another Mac running the exact same build of the OS on the dead machine. I begrudgingly needed to update my Mac Mini to Big Sur to get it to work.
2. Plug a USB-C cable into the front left port of your dead MacBook, fire up Apple configurator on the functional machine and click “Revive.”
3. Wait, hope it works.... but there’s no confirmation so you just have to wait a long time and hope it was long enough, then hold the power button for 30 seconds to see if it’ll turn on.
4. If that doesn’t work (it didn’t), then you should run “restore” which is exactly the same. Wait a long time, hold the power button for 30 seconds and hope. Eventually, in my case, it powered up into internet recovery, and acted as if it were a new Mac. Everything is gone, but it’s at least functional as far as I can tell.
This will ONLY apply to the T2 models, which are not the ones mentioned in the OP, but it seems like a similar issues. These steps at least revived my machine, but it was so obscure that even Apple support didn’t know about this, so ordered a replacement. I can’t be the only one to have run into this, but I’m pretty pissed that I blew two entire days trying to figure out what was going on.
More details on my Twitter: https://twitter.com/ow/status/1328389544119513089?s=21