Does a fast of making up for missed days (Qadaa’) become void due to the emission of pre-seminal fluid (madhy) after watching a medical video about the vagina and childbirth, without masturbation or intending its emission? And does this necessitate expiation?

If what was discharged was semen, then your fast is broken due to repeated looking accompanied by emission, and you are required to make up that day without expiation. A believing woman is commanded to lower her gaze from what Allah the Almighty has forbidden, whether she is fasting or not.