Try reset Office activation status with tool from link: OLicenseCleanup.vbs, the tool can help solve the issue if it is caused by account conflict. Go to Start Menus>Settings>Account>Access work or school, disconnect all your accounts from here, then restart your PC, sign in Excel again and check the result. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.