If you have Microsoft Multi-Factor Authentication enabled, Outlook and other applications may not accept your password. This is due to the application not 'understanding' modern authentication. If you are prompted for a password, then try following this guide to update the Office application first >> Update Office 365 Applications
If Outlook is not connecting and showing a password prompt, use the instructions below to create a single use application
Creating an Application Password
1:Once logged in to your office portal (Sign in HERE) at the top right, click on your little Circle (1) and then Edit Account (2)
2: When this page loads, click on (3) Security Info
3: Click on Add method (4)
4: When this window pops up click on the Drop Down (5) and the select App password, then click on Add (6)
6:Type in a description in (7) for the password, like Outook Password and then click on Next (8)
7:Microsoft will then generate you a password, copy that password (9) and once you have it click on Done (10)
8:You will now see that App password listed, the only option you have is to delete that password.
Note: That you will only every see the password once, when you have created it, it can not be revealed again!