Is Blinken not talking to China because he doesn't want to talk them or Beijing doesn't want to talk to him?
Although Blinken and Sullivan are both hawks, I think Biden listens to Sullivan, since he is actually Sullivan's direct boss. Blinken belongs to State Dept and is not under Biden's control (de facto, due to Biden's weak administration).
It looks to me that since the Alaska debacle, Blinken (Secretary of State) has been relegated to interfacing with allies, a light duty task with captured audiences. Meanwhile, VP Harris, like Biden as VP for Obama, was assigned the task of Latin America. Not that she is being that effective either.
Sullivan (National Security Advisor) now handles the tough jobs like China etc.
Blinken is just weak and useless. He is relegated to making empty tweet proclamation about "America speaking from position of strength."