Request firmware update for startup disk

If you have a third party internal SSD installed and never previously installed Monterey, then reinstall the original Apple OEM SSD & install Monterey so that the system firmware is updated. Then remove & reinstall the third party SSD.....the Monterey installer should now allow you to install now.

Follow the advise from @HWTech

In macOS 12 Monterey and somewhere around version 12.3.

The Apple Installer will check if the Destination Drive is an Apple Original Drive

If it finds an After Market Drive - the installer may present the error message " Firmware update is Required "

By following the previous instructions, the Firmware Update will Flash the Computer with a newer EFI Boot ROM

So once that is done, changing out the Apple Original Drive for the After Market Drive

Run the Monterey Installer again with the After Market Drive in the computer should work

PRP_53 wrote:

In macOS 12 Monterey and somewhere around version 12.3.

It occurred with the initial launch of Monterey, unless another issue was introduced later on that I am unaware.

The Apple Installer will check if the Destination Drive is an Apple Original Drive

The Monterey installer does not care about the actual destination drive. The Monterey installer only requires a working and properly partitioned & formatted Apple OEM internal drive exists for the use of the system firmware updater. Once the system firmware has been updated by the Monterey installer, then the Monterey installer no longer cares about the internal drive.

The macOS 10.13+ installers always use the internal drive as a staging area for updating the system firmware which occurs the first time a particular version of macOS is installed onto the system even when installing macOS to an external drive. The only difference between the macOS 10.13 to 11.x installers and the Monterey installer is that the Monterey installer also requires the internal drive to be an Apple OEM drive.

Firmware updates as a rule come with Security Updates, have you applied all of them?

What are you trying to update to???

Ok, all yours