Generally, the very First Account that was setup on this computer when it was Brand New is the Administrator Account of this computer
That Account needs to logged into allow the upGrade to commence
It is much like on iPhones and iPads where your have to manually input the PIN number before and UpGrade can start.
It it done to insure your are the Owner and Administrator of this device
If you have Forgotten the Admin Account Passwords or do not know it >>
Reset Computer Password for the Administrator Account Password
Intel Computer
1 - Shutdown the computer
1A - Restart computer and immediately hold the two keyboard combo Command r
1B - If using a Bluetooth Keyboard with Rechargeable Battery - Cable the Keyboard to computer for this unique purpose. Bluetooth Kernel may not load soon enough to execute the 2 keyboard commands
2 - Top Tool Bar >> Utilities >> Terminal
3 - Type resetpassword as one word and no spaces
4 - Press Return key
5 - Follow the prompts and remember the New Password
Apple Silicon M1 / M2 Computer
1 - Choose Apple menu > > Shut Down
1B - If using a Bluetooth Keyboard with Rechargeable Battery - Cable the Keyboard to computer for this unique purpose.
2- Do not attempt a Restart to access this feature. The computer Must be Shutdown and pause for about 10 seconds before moving forwards
3 - Press and hold the power button on your Mac until you see “Loading startup options.”
4 - Click Options, then click Continue.
5 - Top Tool Bar >> Utilities >> Terminal
6 - Type resetpassword as one word and no spaces
7 - Press Return key
8 - Follow the prompts and remember the New Password