Did European rulers able to decide whether their countries would be catholic or protestant after the Thirty Years' War?

Yes, after the Thirty Years' War, the Peace of Westphalia in 1648 allowed European rulers to determine the official religion of their respective territories. This treaty reaffirmed the principle of cuius regio, eius religio, meaning that the ruler's choice of religion would dictate the religion of the governed. Consequently, many rulers chose either Catholicism or Protestantism, leading to significant religious and political divisions across Europe.