Short answer: Yes, if your current Windows installation works and you do not need to roll back to the previous version.
What is Windows.old?
Windows.old stores files from the previous Windows installation after a major update or upgrade. It is usually created so you can recover older files or roll back for a limited time.
How to delete it safely
- Open Settings > System > Storage > Temporary files.
- Look for Previous Windows installation(s).
- Read the warning and confirm only if rollback is not needed.
- Use the Windows interface instead of manually deleting the folder.
When to wait
Wait if you recently upgraded, drivers are unstable, apps are broken, or you still need files from the old installation.