Hello Sam Westmacott, thanks for posting this in the community.
If the Windows directory (usually C:\Windows) was moved to the Recycle Bin and emptied, the operating system is severely damaged. If it’s still in the Recycle Bin, do not empty it because you can restore it immediately. First, confirm whether the system boots at all. If it does not, you will need recovery media.
To recover, start by restoring the folder from the Recycle Bin if it is still there. Right-click and choose Restore to return it to C:\Windows. If that does not work, try using System Restore by booting into Advanced Startup, selecting Troubleshoot, and then System Restore. Choose a restore point prior to the technician’s session. If the operating system remains broken, use a Windows 11 ISO to perform an in-place upgrade repair, which will keep your files and apps intact.
Regarding iCloud, it does not back up the Windows system directory it only syncs user files. For full OS recovery, you need Windows Backup, a System Image, or OneDrive PC folder backup.
If your two computers were previously linked through a Microsoft Account, OneDrive, or HomeGroup, sign back into the same Microsoft account on both devices. To reattach the subscription, sign into the correct account under Settings, Accounts, and Your Info.
If none of these options resolve the issue, create Windows 11 installation media by downloading it from Microsoft’s official site. Boot from the USB and select Repair your computer, then choose Startup Repair or Reset this PC while keeping your files. If critical files are missing, use File History or a third-party recovery tool like Recuva before reinstalling.
Kind regards,
John Oli