How do you handle a teenager who has stopped talking to you?
Some withdrawal is developmentally normal — separating from parents is the task of adolescence, and it is not a verdict on your parenting. What tends to keep the channel open: side-by-side conversations rather than face-to-face ones, since driving, walking or cooking together lowers the intensity; responding to small disclosures without over-reacting, because how you handle the small ones determines whether you hear the big ones; and staying available without interrogating. Worth distinguishing from concerning withdrawal — losing friends, dropping activities, changes in sleep, eating or school performance, which warrant a closer look and possibly professional input.
Answers
How you handle the small disclosures determining whether you hear the big ones is exactly right, and easy to get wrong once.
Side-by-side rather than face-to-face is the single most useful thing I have read about teenagers.