A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Could you please confirm whether you're opening your files through the Microsoft OneDrive folder in the Chromebook's Files app, or directly through the OneDrive website in Chrome? Also, are you able to open a newly created blank Word or Excel document? This would help determine whether the problem is related to the Chromebook's OneDrive integration or affects Microsoft 365 web applications generally.
As an additional troubleshooting step, please open Chrome in Incognito mode, visit https://onedrive.live.com/, sign in to your Microsoft account, and try opening one of the affected documents directly from the website. If the file opens successfully, this may indicate that cached browser data or an extension is interfering with Microsoft 365. You can then try temporarily disabling Chrome extensions or clearing the cached data and cookies associated with Microsoft websites.
If the documents work directly on the OneDrive website but still fail when launched through the Chromebook's Files app, another option is to reconnect the OneDrive integration, using the option to remove access and then reconnect your account.