Why did my fresh Windows installation restore files from my old PC?

The Windows installation itself is probably still clean. Signing in with the same Microsoft account can connect the new profile to your OneDrive storage, making your old Desktop, Pictures, and other folders appear. Some files may only be cloud placeholders, while others may already have been downloaded locally. Unlink or uninstall OneDrive, turn off folder backup, and remove the local copies you no longer want. Be careful not to delete cloud files unless you intend to remove them from OneDrive everywhere.

For a genuinely separate setup, create Windows with a local account or keep the computer offline during the initial setup, then add your Microsoft account later only if needed. Microsoft often encourages OneDrive during setup, so check each backup and sync option instead of accepting the defaults. A reset will not necessarily solve this if you sign back into the same account afterward.

Disabling syncing stops future changes, but it does not automatically erase files that were already downloaded to the computer. After unlinking OneDrive, check the Desktop, Documents, Pictures, and OneDrive folders and delete or move only the local copies you do not need. Also check whether old games were restored through another backup or installation service rather than assuming every file came from OneDrive.