If you are sure the disc drive is original, start by checking drive functionality. Does it take in and out discs normally? Is all power rails supplying the disc drive and the power rails on the drive controller board present?
Yes the disc drive board stays with the CPU and SSD boot partition.
Are you sure if the drive is original? If you did not replace it, it’s possible someone else did.
Because they wanted to save $2 per console.
Xbox One boots from an eMMC chip, S/X could do the same and in fact uses the same southbridge chip and has a spot for the eMMC chip, but MS omitted the eMMC and opted to store the core firmware right...