Does the intentional emission of semen during the daytime in Ramadan and the failure to perform ghusl affect the fasting of the days that follow it, or is each day independent, and only the day on which the state of janabah occurred is invalidated?

Not every emission of semen invalidates the fast. If semen is emitted due to a reason that necessitates breaking the fast (such as masturbation or direct contact), then the day must be made up without expiation. The fasts of the following days are valid, and ghusl (ritual bathing) from janabah (state of impurity) is not a condition for the validity of the fast. If the discharge is madhy (pre-seminal fluid), it does not invalidate the fast. If you are unsure whether it is semen or madhy, it is permissible to consider it madhy. It is advised not to succumb to obsessive thoughts (waswasa).