I created an activity template using version 4.2.12 of Activity Generator. When I try to create an activity using this template I get the message

This is an old style template. Please check the route or docs before assuming you can start with cars in the player train.

How do I create a new style template?

I was able to create a new style template by also creating a .pro file. The first .pro file I created was empty. Perhaps because the path had the same name as the activity.