A family of Microsoft word processing software products for creating web, email, and print documents.
If your macOS is below 12, Office products will now enter reduced functionality mode. In other words, the OS is too old to receive the licensing update the Office now requires.
Reduced functionality mode means you can open and print files, but you cannot edit, save or create new files. You don'thave to do anything to enter this mode. It should already enter this mode automatically.
This is an update that occured on July 13th and Microsoft shared it here: https://support.microsoft.com/office/update-microsoft-365-or-office-on-your-macos-or-ios-device-f418ae5d-bb5f-4078-b3d9-9340f5dd084e
If your device cannot update its OS to at least 12, your options will be: Use the web version or an alternative like LibreOffice. And you want to cancel your subscriptions.