A family of Microsoft word processing software products for creating web, email, and print documents.
Please don't do anything until the issue is clarified. It could be due ti a font size issue but could be any of several other causes. The 2nd step from Cherry_Z doesn't work anyway & it probably isn't related to Preferences whatsoever.
First, determine the present Version Numbers of both macOS & Office. Include that information in your reply.
Is the issue with one specific document or are all documents affected?
Please provide a screen shot of the entire document window with the Home tab displayed.