Are there any outdoor Environment available in Isaac Sim especially for the Follow me Application?
No, unfortunately there is no outdoor environment in Isaac Sim at the moment.
We will try to add in the future releases.
Is it any roadmap when outdoor encironement will be added?
You can try to import your own environment into Isaac Sim using Connect https://docs.omniverse.nvidia.com/robotics/text/Omniverse_Connect_Overview.html