Hello, thank you for reaching out to Microsoft Q&A.
If you’ve recently upgraded your device to Windows 11, you have a 10-day rollback period. After this period, the system automatically deletes the files required to restore the previous version of Windows 10 to free up disk space. Once those files are removed, you’ll no longer be able to revert to Windows 10.
In this case, your only option will be to perform a clean installation of Windows 10 using a USB bootable installation media. Please note that this process removes all files and apps during installation.
Reference:
Go back to the previous version of Windows
You will have to backup all of your personal files to an external hard drive and proceed with reinstalling Windows 10.