Step 1: Right click Start > Run > regedit
Step 2: Navigate to the following registry key
HKEY_CURRENT_USER > Software > Microsoft > Office > 16.0 > Common > ExperimentEcs > Overrides
Locate the ‘Microsoft.Office.Outlook.Hub.HubBar’ string value and set it to ‘false’. Then click OK and restart Outlook to check if it works.
Step 3: If the string “Microsoft.Office.Outlook.Hub.HubBar” doesn’t exist, create it by right-clicking on Overrides in the left pane and selecting New > String Value then Paste “Microsoft.Office.Outlook.Hub.HubBar” in the new entry that appears in the right pane
Step 4: Double-click the new name
Step 5: Enter “False” in the Value data field and Click OK
Step 6: Close and restart Outlook