A Rare Windows Activation Problem

Hi, I was tinkering with the 'Change Product Key' Option in Setting: System > Activation. In the 'Enter a product key' dialog box I entered a random key. But, Microsoft Servers gave a rare response to the key. It was a legitimate key. So, in surprise, I activated the device with it. It took a while to install the professional version over the home edition. But, it was after the upgrade I came to know that the key was already in use by someone else and thus the activation process failed but the device upgraded. Now, I get 'Activate Windows' in the right bottom of the screen and can't personalize the device. The device came with a pre-installed and Activated copy of Windows 11 Home. I tried contacting dell support (Chat Code : #30176913 ) through the virtual assistance and I was guided to perform an Operating System Reinstall . However, the reinstall comes with user data loss. So, How can I have an offline backup  of my files, installed applications and other device settings so that the professional edition problem doesn't returns on restoring using the backup ?