I’m also experiencing the problem. I can send a test email from the site (via the Wordfence plugin) and it works fine and the email has the template applied to it. But when I use the Email Templates “Send test email” function, I don’t get the email.
I turned WordPress debugging on and checked the logs, but did not see any problem there.
The site is running the current versions of WordPress (5.8.2), Email Templates (1.3.2.1) and PHP (7.4.26).
If there is anything else you’d like me to test or information to provide please let me know. Thanks!