I did some scientific test and got a rough conclusion:

The boot drive has a chance to be undetectable by the mother board. I assume it's the physical connection issue.

Based on my test result, the chance has a high correlation with the tightness of those screws on the back lid.

Open the lid, the boot drive can be detected every boot.

Close the lid but don't tighten the screws, same result.

Partially tight the screws, also stable across every boot.

Tighten the screws with hand, as far as I can tell, it's stable.

Tighten the screws for about 0.5Nm using a screw driver, the boot drive is undetectable.

And the error "a bootable drive has not been detected" doesn't mean your boot partition is broken. Apparently, it can also literally mean there is not a boot drive showing up. The data on the disk is fine, but the disk is missing. I though it's the boot partition is broken or something.
----
BTW, it's a cheap Kingston 500G NVMe disk. It feels cheap, it bends cheap. I assume it's the over-tightened screw bends the disk and causes some connection issues on the m.2 connector.