Parentheses are the tone and expression on the screen, the fast-paced and efficient cooperative courtesy, and the courage and outlet left for yourself when chatting. I don't know when brackets became a common symbol in the context of social networks. It can be complete or only half "(), but the function is the same.
When we chat face to face in reality, we will receive all kinds of nonverbal communication information except spoken language, such as judging whether the scene is appropriate from the volume.
We will not talk loudly in the quiet library, nor will we discuss gossip in the conference room. Sometimes putting brackets on WeChat is an imitation of lowering the volume and whispering in real speech situations, which can show the inappropriateness of the situation and infer the emotional state of the speaker.