A family of Microsoft word processing software products for creating web, email, and print documents.
If your Mac isn't able to run a version of macOS newer than High Sierra the last available update of Mac Office is 16.43.0 - there is nothing that can be done to change either of those limitations. Exactly what is it that you expect to be able to do other than invest is a newer Mac?
I understand that doing so may not be possible for everyone but obsolescence is an unfortunate reality of the computer world. The good news is that the current configuration will continue to be usable until the hardware finally dies, it simply cannot be updated beyond its present state.