Contact support. If your machine is out of warranty, you can pursue either mainboard replacement at cost, reflashing the firmware manually (with the appropriate programmer) or having somebody on the forum or at a repair shop do the same at moderate cost.
(If you’re in the St. Louis area of the US, I’d be happy to do it for a coffee ;P)
Surprisingly this happens more often than people realize.
Some vendors would not update the BIOS on laptops with less than 30%-50% charge for this very reason.
Since Framework boards can be standalone a different logic would have to be in place to put this additional protection in or at the least warn the user they are about to perform a BIOS update and the battery is either not present at all (standalone) or below X state of charge.
Further complicating things is requiring user input when there are cases the BIOS update needs to happen by just the UEFI shell automatically when trying to recover from a bad flash.
It would be nice to have a primary and backup BIOS like some motherboards have; this adds cost and complexity though.
To prevent this I suggest using a 60W+ powerbank capable of input and output power at the same time. Be careful though, some powerbanks claim of doing so may reset to 5V upon plugging in the second input. Make sure to test them before powering a BIOS update
Right, that is what I was thinking. Except the OP stated it as a laptop so it definitely has a working battery to function as a laptop. My estimation is the battery was low or critically low, the power went out and…crickets
Too bad the EC couldn’t be talked to over the diagnostic port and have it automatically try to flash the BIOS if it was started up (like the power button is pressed and held for 10 seconds upon power up) to trigger looking for a USB device on a specific port and then reading and flashing the BIOS like what can be done on some Asus motherboards. I think they call that feature “flashback”. It is on a specific port on the back of the motherboard and I think a button has to be pressed and held or something to trigger it.
I had to do that a few years ago when 14th gen Intel processors came out but motherboards did not know how to talk to the newer gen processor and if you were building a new machine you probably didn’t necessarily have a 12th gen processor to just slap in it just to update the BIOS to be able to boot the 14th gen Intel processor freshly purchased.