I see. So you live in Europe and your goal is not to learn how the US Constitution stipulates that Congress, not POTUS, determines the number of justices, but to spread misinformation in the US, presumably with the goal of creating political division.
Who decides how many Justices are on the Court? Have there always been nine?
The Constitution places the power to determine the number of Justices in the hands of Congress. The first Judiciary Act, passed in 1789, set the number of Justices at six, one Chief Justice and five Associates. Over the years Congress has passed various acts to change this number, fluctuating from a low of five to a high of ten. The Judiciary Act of 1869 fixed the number of Justices at nine and no subsequent change to the number of Justices has occurred.