If you are going to buy illegitimate not for resale keys for office (groupon, fake news sites etc), I found a really cheap site that works:
https://www.gamers-outlet.net/Coupon code SOFTCHAT10 for 10% off.
I upgraded my pc from win11 he to pro for: 4.75
Installed 2021 pro plus lifetime for 5.09 (phone activation) and both worked... The win 11 pro should survive a reinstall as I see the license reflected in Microsoft account. Office is prob only good for 1 installation (or two if you are fast).