Hello,
Your PC is just stuck in demo mode. I guess the store didn't take it out of demo mode before they sold it to you.
To remove demo mode, go to Settings > System > Activation and then click on the text next to the Windows icon (should say something like "Windows 11 Home" or "Windows 11 Pro") 5 times and then in the window that comes up, push "Advanced configuration" and then click the "Remove" button next to "Remove RDX". Push "Confirm" in the window that pops up, and then your PC will restart and allow you to set it up as your own.
Let me know how this goes.