Before generating the app password, you have to enable 2-step verification.
Go to your Google My Account
After that, scroll down and select an App Password option.
Note:- If the 'App Password' option is not showing, then please wait for some time (around 10 minutes or more) to get changes reflected on Gmail servers and then visit: https://myaccount.google.com/apppasswords to create the app password.
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