Thanks for reporting this bug we will remove none option from there.
Actually you have selected "Encryption Mode - None" for swift-mailer.
And swift mailer does not support encryption none .
so you just need to locate and open file swiftmailer.yaml under
config->packages in your project.
Now change encryption to tls or ssl instead of none as per support by your email server and save your file.
Now run your project and error will be removed.