Hi, I'm Bernard. I'm happy to help!
Just to confirm, did you change or replace major hardware on the PC before reinstalling it? Did you reinstall it from scratch by using Windows 11 Bootable media?
Note: Before doing any steps, verify the version by going to:
Settings > System > About
Under Windows specifications, check the Windows Version and Edition.
Step 1. I recommend upgrading back by following the steps below:
Go to this link: ms-windows-store://pdp/?productid=BF712690PL0G&OCID=windowsproupgradesupportpage
Click Open to open Microsoft Store, then select upgrade to Pro
Note: Make sure you are signed in to the account you used to upgrade to Windows 11 Pro.
Method 2. Upgrade using Windows 11 default key:
Open Terminal (Admin) or Command Prompt (Admin), then install the default product key for Windows 11 Pro:
Copy, paste, and Enter:
slmgr /ipk VK7JG-NPHTM-C97JM-9MPGT-3V66T
Additional note: These sets of methods will only work if you have a valid digital license of Windows 11 Pro.