DRS works like in real F1.
Take a look at this thread to learn where they are located:
https://igpmanager.com/forum-thread/43412
When you are following another car and your gap is less than 1 second at the beginning of DRS zone, you have DRS. If you don't have any car in front of you in 1 second range, you won't get DRS. That's how it works.