If ejaculation occurred before Fajr of the night of Ramadan but Ghusl was still not done until after Fajr, will the upcoming fast be valid?
Bismihi ta'ala
If one had enough time, and intentionally did not perform ghusl before Fajr time, then their fasting for that day will be invalid, and they must redo that day as qadha` and pay kaffarah.
If they did not have enough time, or it was not intentional for them to stay in janabah, then their fasting is valid.
And Allah knows best.