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