Microsoft 365 credential prompts on Outlook® LTSC MSO (Version 2408 Build 16.0.17932.21000

Because the credential loop began after the LTSC update, the build change is important evidence, but it does not by itself confirm a known regression. Start by testing the same affected account in Outlook on the web and on an unaffected computer. That separates account or tenant authentication failures from this client. Record the complete Outlook and Windows versions, the prompt text, error or correlation ID, and whether other Office applications also loop. Ask your administrator to review Microsoft 365 service health and corresponding sign-in failures. Then run Microsoft’s Microsoft 365 Sign-in troubleshooter on one affected device before applying changes broadly. WAM package repair is a documented remedy for specific missing-package symptoms, not a reason to delete token folders indiscriminately. Avoid disabling modern authentication or MFA. If the issue remains, submit the affected versus unaffected build comparison to Microsoft support for a targeted workaround.