Thanks for the suggestion. Your insight pointed me in the right direction. And I tried on another computer, with a fresh Google USB driver, and the phone was able to be seen to Unlock the bootloader from the GrapheneOS web installer page.
_"Unlock the bootloader to allow flashing the OS and firmware:
The command needs to be confirmed on the device and will wipe all data. Use one of the volume keys to switch the selection to accepting it and the power button to confirm.
<Unlock bootloader button here>"_
And I was then able to do the important step below.
"Replacing GrapheneOS with the stock OS
Installation of the stock OS via the stock factory images is similar to the process described above but with Google's web flashing tool. However, before flashing and locking, there's an additional step to fully revert the device to a clean factory state.
The GrapheneOS factory images flash a non-stock Android Verified Boot key which needs to be erased to fully revert back to a stock device state. Before flashing the stock factory images and before locking the bootloader, you should erase the custom Android Verified Boot key to untrust it:"
<Remove non-stock key button here>"
THANK YOU SO MUCH! GREAT KARMA SENT YOUR WAY!