Hi @ppmoreau ,
Course navigation includes all published courses, not only those the user is enrolled in. Although the user can navigate to the second course, they will not be able to access its lessons unless they enroll in it.
If you don’t want the user to see a link to the second lesson, the best solution is probably to hide the course navigation entirely with CSS.
You can hide any element on the page using a CSS rule as described here:
https://css-tricks.com/video-screencasts/142-hiding-things-with-css/
That said, since this would require custom code, we’re not able to futher assist with this.
Hope that helps!