Currently, access cannot be restricted by level of competency. The workaround is that you restrict access via activity completion by referring to the activity that grants certain competencies. This only works on course level, not on a global scale. So if you get a competency in one course or activity, and another course or activity should only be accessed if you have obtained certain competencies, there is no way of restricting said access. This makes it impossible to set up a competency-based learning environment in Moodle.