Hi @kharazzi! A few comments, as you can expect... ;)

As you said, dark matter actually first appears at the end of the 19^th century, by Poincaré. However, there was everything but an agreement on that at that time (Kelvin and Poincaré strongly disagreed with each other).

This being said, the modern vision of dark matter dates from the 1930s, and is completely different from what was thought 120 years ago.

To learn what the composition of dark matter is, scientists, investigate some familiar material in the universe, such as Baryonic material that has protons, neutrons, and electrons. Dark matter can I be made of the Baryonic material or even vice versa.

Actually not. Dark matter cannot be made of known particles. It can be baryonic, but it is then different from the baryons we know.

Finally, dark matter has not been found, and there are alternatives without dark matter. Those alternatives, even if the evidence is sightly weaker, are still very alive.