Are you able to physically replace the HDD (preferably with an SSD)? If so, you can use the (Win10) Media Creation Tool to create a USB installer.

When it prompts for a key, just skip it. If you have an OEM mass activation laptop (i.e. anything from a major brand), it’ll activate automatically after. If, for whatever reason it still doesn’t activate, you’ll have a nag screen telling you to activate. It won’t significantly limit what you do.