Hi @ojoong kwon ,
Glad to hear this issue has been resolved!
Thanks for the sharing.
However, due to a recent update in forum policy, the question author now is not able to accept their own answers.
So I have written a brief summary of the solution this issue. Please feel free to accept it as the answer, which would benefit others who also has similar issues in forum.
Issue:
Search not working normally in Outlook 2016
Solution:
After adding the below registry key, the problem was solved.
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\Search << DisableServerAssistedSearch(DWORD32, value 1)