Word for the web does not open. Documents remain on a loading spinner indefinitely.

Your tests already isolate this beyond one document, browser or network: even newly created Word documents fail, while Excel and OneDrive work. I would not repeat cache clearing or disable more browser protections. The console CORS message alone does not establish the underlying cause. One useful remaining comparison is to try a new blank document with a different personal Microsoft account in a separate browser session, and try your affected account on another device if available. Record those outcomes and a UTC failure time. Then use Microsoft’s Get Help route for personal accounts, describe the Word web loading failure, and select Contact Support when offered; available contact methods depend on the product and subscription. Include your existing browser/network tests and the failing request details. This needs service-side investigation if the failure follows the account. Keep downloaded copies of important documents while awaiting a supported resolution.