I call bullshit. What's your source?

Blow up might not be exactly right, but I could imagine smoking a chip or some other method of frying some electronic component. If you send 12v by mistake down a line connected to a component only expecting 3.3v or 5v, then it could easily fry it. I'm guessing most components at this stage of the board have been assumed a good voltage and might not have anything inline between the M.2 connector and the component to spill any extra volts.

If you google "m.2 pinout", you'll find that none of the variants use 12V and 5V on the same pins. It's almost like the people who design these things know what they're doing.

But some use 3.3 volts or gnd on pins that others use as data output pins. That will blow up the output driver MOSFETs.

Doesn't mean someone buying a connector like this to DIY their own thing know what they are doing

That's a truism. You could say that about any connector.

I've personally toasted 2 x M.2 NVME Boards confusing them with M.2 SATA. The key was close enough that I didn't realize the expensive error.

You mean you forced an M-key drive to go upside down into a B-key slot despite the misalignment of the key?

I think I've only ever found B-key slots in adapter cards that have one M-key slot for an NVMe drive and one B-key slot for a SATA drive, but it would be hard to miss the distinction when they're right next to each other like that.

Thanks, TIL!