I’m pretty surprised no one has mentioned bitlocker. If you have bitlocker enabled then everything is already encrypted. Well at least everything since bitlocker was turned on.
In that case. Just reset Windows (full/factory/wipe) and give it away. Don’t log in, just get it to the “welcome to windows” and shutdown.
Once the original bitlocker key is wiped anything remaining is just randomized garbage.
Whoa. Home doesn’t offer BL? That’s annoying. Then use the veracrypt whole disk option and throw away that key.