Can you try running this command to enable the admin access:
net user Administrator /active:yes
This would basically enable built-in admin account, using that account, you can enable the standard admin account and hence retrieve lost admin access.
In case if still persists, you can try FIX 2 mentioned here:
https://www.kapilarya.com/solved-lost-administrator-rights-in-windows-11
Let us know if this helps!
Note: Included link(s) in this reply refers to a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.