Never install a custom OS on a drive containing data you haven't backed up elsewhere.
Before you look for that .zip or .iso file, remember that "Ultralight" means things are missing: Download Windows Ultralight (22621 590) FBConan zip
If the uploader provided MD5 or SHA-1 hashes, check your download against them to ensure the file wasn't tampered with. Never install a custom OS on a drive
These ISOs usually bypass TPM 2.0 and Secure Boot requirements, making them popular for older hardware. The Trade-offs: Is it Right for You? Download Windows Ultralight (22621 590) FBConan zip
Because these are modified versions of copyrighted software, you won't find them on official Microsoft sites. They are typically hosted on: