How to install your Office Home and Business 2021:

Please log in here with your Microsoft account (Hotmail, Outlook…)
https://redeem.microsoft.com/?wa=wsignin1.0

To download your Office, enter the key to redeem it with your Microsoft account (link it).
After linking the key to your Microsoft account, go to this link:
https://account.microsoft.com/services/?OCID=PROD_Office_CONS_MyAccount_Migration&refd=setup.office.com

Then click “Install”, download the setup, and install your Office.
Congratulations, everything is ready.

ALWAYS SAVE THE MICROSOFT ACCOUNT THAT YOU HAVE USED TO DOWNLOAD OFFICE HOME AND BUSINESS 2021 AS IT REMAINS LINKED TO THE KEY.

ALSO SAVE THE KEY THAT THEY GIVE YOU ON THE PAGE
https://account.microsoft.com/services/?OCID=PROD_Office_CONS_MyAccount_Migration&refd=setup.office.com

IN CASE ONE DAY YOU FIND OUT THAT YOU HAVE TO ACTIVATE IT AGAIN OR WHATEVER,
YOU CAN ALWAYS CHECK THAT YOUR OFFICE IS ACTIVATED BY GOING TO WORD > ACCOUNT,
Then you will see that your Office is activated.