Microsoft® Outlook Indexing Options Greyed Out and
Advanced Search Fields in Microsoft Outlook are Disabled or “Grayed Out”
you need to make sure “Desktop experience” is installed on the terminal , Windows search service is running and the following registry key are in order :
PreventIndexingOutlook under HKLM/Policies/Software/Microsoft/Windows/Windows Search as 0
SetupCompletedSuccessfully under HKLM /Software/Microsoft/ Windows Search as 0
you need to reboot the terminal after this changes