How to recover my outlook emails?

Four or five days ago, I started to see all my old emails disappeared. I have checked all my folders including the junk, the deleted, the archive, I've found nothing has been moved there unintentionally. When I ran a search, I could see a whole bunch emails as early as 2016, but none for the period of Oct 23 to Nov 20, 2023. Can anyone tell me what has happened, and how, if possible at all, to get my emails back? Thank you. -Pujing