how to import all the emails from outlook 2011 to the new Outlook app (from appstore)?

Hi!

I have updated my mac OS system (from Sierra to the latest one) and had to download the bundle of Microsoft 365. If I simply import them, as the system guides me automatically, I only get emails from yesterday... Unfortunately Outlook doesn't import all my emails from the old Outlook 2011.

Do you have any advice on how to succeed in importing them?

Thank you!