configuration>email account

i also created app password from gmail and add into the configuration email account but when i send test mail then i got this error : 534: 5.7.9 Application-specific password required. Learn more at 5.7.9 https://support.google.com/mail/?p=InvalidSecondFactor x1-20020aa79a41000000b005769ccca18csm5517500pfj.85 - gsmtp. i created once twice and thrice to work it on but cannot work if this is a bug of your system please check it because i follow all the procedure of you noppcommerce and other sites.

It's not a nopCommerce 'bug', it's a Gmail security requirement.
Do not enable 2-step verification, just create an app password.
(i.e., if you need 2-step verification, then just disable it for now until you get the app password to work)

https://support.google.com/mail/answer/185833?hl=en