As far as I can tell, G-Suite is different (and maybe regular gmail has changed as well). I read lots of posts on how to get an "app password" from gmail, but the screens described in those posts don't match what I see in the G-Suite administrative panel. I was able to get Thunderbird to work with the mail account, but with the same data entered into TCC's option dialog, Google rejects the SENDMAIL data and sends me a warning that an app may have tried to hack my account.
All my other email accounts are hosted by TigerTech, and everything can be done very easily there. And whenever I have a technical issue, I just write to support and get a 100%-on-target reply almost immediately (I love them as I do JP Soft). Unfortunately, they -- for very good reasons -- will not let customers send mail with a FROM field that uses a domain name that they do not control.