There are a few common reasons why Gmail users may have trouble in configure Outlook with Gmail's IMAP or POP feature. Here's a troubleshooting checklist:

 

- Have you enabled POP or IMAP in Gmail?

Sign in to the Gmail web interface.Open the 'Forwarding and POP/IMAP' tab on your 'Settings' page, and configure IMAP or POP. After enabling this in Gmail, make sure you click 'Save Changes' so Gmail can communicate with your mail client.

- Allow less secure apps(Outlook) 

Scroll down to the bottom and find "Allow less secure apps" , turn it on.

https://myaccount.google.com/security

 

I look forward to hear from you to see if the issue is solved.