Why to activate Windows 11 after reinstalling from USB flash drive?

Because I had malware on my Windows, I reinstalled it with a USB flash drive.

When prompted for a product key, I skip it which allowed me to navigate to Windows 11. Now that I want to activate Windows, the BackupProductKeyDefault stored in the Registry Manager is not working.

Clicking “Troubleshoot” does not help:

And here, clicking “I changed my hardware recently” leads to this dead-end (which has an odd old policy by the way)

How can I activate Windows?