These tools actually work with Office 2021 (tested):
The search for a in 2021 was a common task for users needing to recover lost product keys before upgrading systems or reinstalling software . While newer versions of Office (Office 365 and Office 2019/2021) have moved toward account-based activations, key finders remained a vital tool for managing legacy perpetual licenses. The Role of Key Finders in 2021 ms office key finder 2021