A family of Microsoft word processing software products for creating web, email, and print documents.
There is no Export command in Word. Are you trying to create a duplicate file, a PDF, something else? Please be specific about the steps you are taking & what you are trying to accomplish.
Are you using Legacy Comments or Modern Comments?
Additionally, always indicate the specific Version Numbers of both macOS & Office. Those bits of information can make a big difference.
BTW: There is no FILE tab in the Ribbon of Mac Office programs. Any reference to it pertains to the Windows version of the program.