Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Go to Settings, Apps, Installed Apps. Find Office in list, click on 3 dots at right end and choose Uninstall. Follow through to get the app uninstalled and restart. Then go to Microsoft Store and install Office again - I found this worked and the list of files was available again.
(lower-left corner), and select Apps and Features on the pop-up menu.