Point # 1A - There are reports appearing on the ASC Forums regarding failed installation of Monterey on older Qualifying Apple Computers. In most cases this is related to having a NON Apple Original internal drive ?
The EFI Boot ROM included in Monterey is verifying for Original Apple Drive and if not found , may Balk or fail to upgrade to Monterey.
Reports indicate the EFI BOOT ROM is Required to Flash the Computer and is a requirement for a Successful Monterey Installation.
A possible solution is to swap out the drive for an Apple Original Drive and install Monterey to the Apple Drive.
The reverse the switch back to the After Market drive and run the Monterey Installation too this drive.
This solution was by one of the Contributors in this question :-))
EDITED