Challenge question

Is there a way to make a challenge for a circuit where you race a time trial ghost?

You can, but you can't add a constraint for that. Just put the time trial constraint and make a ghost.

Is the win condition beating a specific recorded ghost?

I don't think there's a win condition for that. But, you can just make the win condition to get a faster time than whatever time it takes for the ghost to finish the race.

For example, if the ghost takes one minute and thirty seconds (1'30) to finish, you just put the win condition as finishing the track before 1:30