A full write-up on "pre-activated" ISOs involves understanding their composition, security risks, and the technical methods used to create them. What is a "2021 Update" ISO?
If you must use Windows 7, it is safer to download an "untouched" official ISO and update it yourself: How to get updated windows 7 sp1 iso? windows-7-ultimate-sp1-update-2021-preactivated-iso-gratis
Often used in "All-in-One" (AIO) versions, this uses a local service to manage activation. windows-7-ultimate-sp1-update-2021-preactivated-iso-gratis
The most common method, which mimics an Original Equipment Manufacturer (OEM) BIOS signature to trick Windows into thinking it is on a licensed machine. windows-7-ultimate-sp1-update-2021-preactivated-iso-gratis