Hi, Mircohan, Thanks, for the hint. Under "Turn on Do Not Disturb", the option, "When mirroring to TVs and projectors" was checked and I use external monitor with my MacBook. Unchecking the option solved the issue however, now I get loads of notifications which I don't want to receive! Anyway, the issue is resolved for now with some nuisance.

Running MBP 16'' M1 MAX with macOS Monterey 12.1 (21C52) and MS Outlook for Mac 16.56 (21121100). Tried all the options including, https://support.microsoft.com/en-us/topic/outlook-for-mac-search-returns-no-results-and-task-items-are-not-displayed-cf6eb856-ed4f-54e9-3ef2-546046d87c7e but as some of the folks have mentioned here already, few Emails shows up in the Outlook search result during the re-index and the search result goes blank again after the re-index is finished. Apparently, I can see the Emails being searched in the Spotlight search results but not in the Outlook search!! This is frustrating. Had no issues with my previous MBP and Outlook.