
As Bob said, it's usually best to bear the pain and migrate to a new user account.
The first question that comes up is "What can make a user account go bad?" One thing I can think of that could cause this situation is a file system that needs repair. That leads to my first piece of advice: run a robust disk maintenance utility. Use it to verify the startup volume and all attached volumes. Before doing any additional troubleshooting, make sure the file system is OK. Another possibility is a bad memory block. Mac OS will automatically not use such a block, but anything stored in that memory segment is no longer available.
The second question is now that you have isolated the problem to a faulty Mac OS user account, "What should I do about it?"
You might reinstall Mac OS, but do NOT choose the erase option:
Reinstall macOS - Apple Support
Now decide what to do with the problem user account. You might try to fix it. If you are an expert and/or are lucky, one or two people who had a problem with their user account managed to figure out what was wrong and fixed it.
You know that everything works in a new user account. The installation of Office is fine. If it were me, I would migrate my files to the new user account and then delete the bad one in Mac OS System Preferences and be done with it.
Before transferring your document files, copy your user data from our old user account to the new one. Use the corresponding file locations when copying files to the new account’s locations. Here’s the default location of your templates and user files, but be aware that you may have set other locations in Word > Preferences > File Locations.
To get to the Library folder, in Finder, in the Go menu choose Library.
Library/Group Containers/UBF8T346G9.Office/User Content.localized
This link explains how to transfer files from one user account to another