Microsoft maintains a comprehensive history of older versions of software that may boggle your mind in its scope. 

 - https://macadmins.software 

You can see they’ve hi-lighted minimum system versions and there is a cut off for Mojave as it’s fallen off the “current release train”.

You’ll want Word downloaded from the 10/12/21	16.54.0	21101001 line of office releases if you can’t download it as a previous purchase from the Mac App Store. Below are the full suite installed and word update direct downloads from Microsoft. 

- https://officecdnmac.microsoft.com/pr/C1297A47-86C4-4C1F-97FA-950631F94777/MacAutoupdate/Microsoft_Office_16.54.21101001_Installer.pkg
- https://officecdnmac.microsoft.com/pr/C1297A47-86C4-4C1F-97FA-950631F94777/MacAutoupdate/Microsoft_Word_16.54.21101001_Updater.pkg