Hello, thank you for reaching out to Microsoft Q&A.
It’s possible that the hackers deleted all of the emails from your Inbox folder.
Have you checked whether the emails are available in the Deleted Items folder instead, or in the Recoverable Items section of that folder?
If there are no emails in that folder, unfortunately, your emails have been permanently deleted and there is no way to recover it.
Alternatively, sign in with your Microsoft account here to see if there are any unusual activity in your Microsoft account -
https://account.live.com/Activity
If you see any unusual signs in,
1. Reset your Microsoft account password.
Open an InPrivate/Incognito browser window and use the following link to reset your password: https://account.live.com/ResetPassword.aspx
2. Sign out of your account from all sessions.
Once the password reset is successful, sign in with your account here: https://account.live.com/proofs/Manage
Scroll down until you find Sign out everywhere. Select Sign out everywhere.
3. Enable two-step verification.
On the Security settings page, under Additional security, turn on Two-step verification. Make sure you have at least three security verification methods active.
After you have enabled these security protections, sign out of your account in the Outlook app and sign back in with your new password.