Without any logs it's tricky to know where the issue is, have you confirmed that outbound SMTP ports 25, 465, 587 are open to send email? Are you running this on your local development environment or a hosting provider environment?
Make sure you are running with dev mode on, so you can see verbose information in the logs and full stack trace errors. The knowledgebase article you linked might be a bit misleading as I believe it's referring to the error output from a Craft CMS 2 website, not a Craft CMS 3 site.
The log file you need to look at is
/storage/logs/web.log. When debugging is enabled, this file gets very verbose quickly. The best thing would be to completely clear it out and then do your SMTP test to see the specific error occurring without having to scroll through a lot of verbose info.
Equally are there logs on your SMTP providers side when you attempt to perform an SMTP request from Craft CMS? I'd guess not, given Craft CMS is throwing an error, but just in case it's at least making a negotiation to the SMTP server.