Enable IMAP in Gmail:
Open Gmail
Click the gear icon
Select See all settings
Go to the Forwarding and POP/IMAP tab
Enable IMAP
Save changes
Prepare your Gmail account:
Turn on 2-Step Verification
Generate an App Password in your Google Account
Open Outlook
Go to File
Select Add Account
Enter your Gmail address
Choose Advanced options
Select Let me set up my account manually
Choose IMAP
Enter incoming mail server settings:
IMAP server: imap.gmail.com
Port: 993
Encryption method: SSL/TLS
Enter outgoing mail server settings:
SMTP server: smtp.gmail.com
Port: 587
Encryption method: STARTTLS
Enter your Gmail username
Enter your App Password
Click Connect or Next
Finish the setup
If needed, adjust Gmail settings in Outlook:
Set outgoing server authentication to required
Use the same username and password for sending mail
Sync folders after setup
If setup fails:
Recheck IMAP is enabled
Recheck the App Password
Confirm ports and encryption settings
Update Outlook to the latest version