There have been lots of requests in the past for distance counters and finish lines for all courses. Only a few have them built-in. But there is a way to get a distance counter and a finishing splash screen for every course in Zwift, by using the Meetup function. If you create a Meetup for yourself, your ride will be treated like an event and will include a distance counter and a finish line.
It isn’t particularly convenient nor spontaneous, but it works. The earliest start time will be 6 minutes in the future, and you MUST invite at least 1 other Zwifter. We all spend a few minutes prepping for our rides anyway. And I know someone who has an account but never uses it, so I would invite them.
I’ve been Zwifting long enough that the distance counter isn’t such a big deal for me, but if I wanted one this is how I could get it.