don't go for those super cheap $2 or $3 options; they might be part of some shady stuff and could get yanked at any moment. I've never bothered buying a legit Windows key 'cause it's so easy to crack, but I had to buy Office 2021 and i dropped around 40 bucks for it . The good thing was, it wasn't one of those OEM keys, so I could link it to my Microsoft account using https://setup.office.com. That way, I can change my hardware whenever I want, and no one can take it back. Luckily, when i was looking I stumbled on https://keysomatic.com/ on Google Shopping when I needed to activate it.