Was this computer a Brand New computer at time of purchase ie From: Apple Directly and in a sealed plastic Wrap.
There have been some very interesting development especially when it comes to Apple Silicon Computers
There is a difference between an Owner Account and an Admin Account
The " Owner Account of this computer " has that privilege to add, remove, upgrade or downgrade accounts. This would include adding more Admin Accounts and / or downgrading an ADDED Admin account
Set up users, guests, and groups on Mac
Normally the " Owner Account " is the very first Account used when the Computer was Very First Setup as New and out of the box.
Adding additional Admin Account can be done there after.
Below link all provide additional insights about the Difference between Admin Accounts and Owner Accounts
https://eclecticlight.co/2021/07/18/last-week-on-my-mac-the-perils-of-m1-ownership/