TL;DR: The most common fix is re‑registering the AAD Broker Plugin via PowerShell. Jump straight to Solution 3 to get back into Outlook quickly. If you’re staring at the error “A required authentication broker is missing” while trying to sign in to the Outlook desktop app, you’re not alone. This issue has been frustrating Microsoft … Continue reading Fix: “A Required Authentication Broker is Missing” in Outlook & Microsoft 365