Hi, I'm Diane and I'm happy to help you today.
Who is your email provider? The only contacts you'll have in the new Outlook at this time are ones in Microsoft accounts, gmail, yahoo, and icloud.
New Outlook doesn't support importing or local cache so you can only use contacts stored in mailboxes.
If you were using Mail before, you need to go back to it to get the contacts.
If you want to switch back and the switch is missing in the title bar, this article has the instructions to revert to Windows mail or Outlook for Windows:
https://support.microsoft.com/office/toggling-out-of-the-new-outlook-for-windows-preview-ec102b39-5727-418e-ae1f-a1805434640c
The new Outlook is a work in progress - you can leave feedback and suggestions in the Feedback forum. Or, if a suggestion exists, vote for and comment on it.
https://feedbackportal.microsoft.com/feedback/forum/89a8afa3-2e1c-ec11-b6e7-0022481f8472
Let us know how it goes, we're here to help you further if needed.
-- Diane