1. Go to a course
2. Go to participants
3. Go to enrol users

The popup you see here, looks like screenshot 1.

Now go to 'participants' and click the gear at the end of the row of the user you just enrolled. The screen you see now, is screenshot 2.

The screen could/should be the same. My teachers are now complaining that it takes a lot of clicks to enrol someone in the course starting next week. They have to go through both screens to do so.

All the available options should be in one screen, and I think that's possible.