You mentioned trying reinstalling the program. Do you have administrative rights on your computer? I'm not sure but that might have hampered the install if you don't.

Did you try running the Repair feature? I'm on a different version so I am not sure exactly what that looks like, but go to Control Panel, Programs, Programs and Features. When you find your Office programs (in my 365 it's "Microsoft 365 apps for business - en-us") instead of uninstall you'd choose Change, and it gives you the option of Quick Repair or Online Repair. I generally try Quick first, then if it doesn't address the problem, I try the other one.

However, I haven't had your problem, but a couple of times upon an Office update, I've lost all of my pinned files in both Word and Excel and all my document history got wiped clean. Which is slightly annoying but not as disruptive as losing your dictionary. I have a bunch of industry-specific words saved in mine, and when I got a new computer a year ago, the dictionary was the one thing I hadn't copied over. It took a while to get most of the place names and soil types saved again.