Female colleagues are very enthusiastic about me at work, or always smile at me when they talk. Wechat generally responds quickly, but jokes are of little significance.

Nothing interesting. She's just teasing you. Don't take her enthusiasm as her affection for you. Smiling is usually polite to people, and there is no formal address for you. It can also be understood that she doesn't take you seriously Just like when you are facing children, there are usually few formal titles. Maybe she can reply to others as quickly and talk more than you. So you think too much.