There could be multiple reasons for emails not being sent. But we need to be sure about what is primarily causing the issue. It can be either the plugin or the hosting.
To be sure about that the plugin is sending the emails, you can install an email login plugin. We use Email Log plugin to test the features. It is very simple and easy to use. So, after installing this plugin and enrolling a course or completing a quiz, you do not see any emails logged, that means there is a problem with the plugin. Please send us and email explaining the events that are enabled in the settings but still not sending emails.
If the emails are there in the log but you do not see them in your mailbox, please check spam and trash sections first. You can also try searching the words to be sure the mails are not filtered in any way. If you can totally not find the emails, there could be an issue with your hosting provider. You will have to contact the hosting support in that case.