For fixing Calendar entries still missing / Search returning 0 results in Outlook Search, despite search index being rebuilt and Outlook data selected as pool of data for search source, go with a pass of deinstalling/reboot/reinstallating the feature.

That is :

DISM /online /disable-feature /featurename:SearchEngine-Client-Package

reboot

DISM /online /enable-feature /featurename:SearchEngine-Client-Package

reboot

After the restart, go to the control panel / Indexing options / advanced / Rebuild / OK
When the Indexing is completed, close Indexing Options window and open Outlook, test searching.