As you know, LearnDash doesn’t offer a full range of action/filter hooks. The only way to trigger an automatic enrollment without going to the course page is with a “trick”, as follows.

To manually trigger an auto-enrollment, place the following code on the first page your members see after login you to simulate a visit to a LearnDash post/page:

This hidden shortcode will not display anything on the page but will trigger the LearnDash enrolment functions for any course in which the user should be automatically enrolled.