In a sense, humanity has long been capable of transmitting interstellar messages (METI (messages to extraterrestrial civilizations) - attempts to transmit interstellar messages from humanity to probable intelligent beings outside the solar system.)
The first strong generalization sent into space was probably ... Hitler's speech.
This short television program, literally a few minutes, was broadcast in 1936 from Berlin with the opening of the Olympic Games. Although it was only received in Germany, it was the first, albeit weak, transmission from Earth. Unlike conventional radio broadcasting in the 1930s, TV signals pierced the ionosphere and went into space.
After that, the broadcast of the coronation of George VI took place in England and something else of the same kind. Truly television began only in the late 40s. And all the signals of those years are carried away from the Earth at the speed of light.
However, all of these signals are extremely weak. After passing only a couple of light years, they will fade out and it will be almost impossible to catch them, much less decipher.
The main problem with sending interstellar messages is that as the distance traveled increases, their power gradually decreases due to gradual scattering (diffraction). Imagine that you have thrown a stone into the calm surface of a lake: from the original stone the circles began to diverge in all directions, but the further they diverge, the less noticeable they become. The same thing happens with radio waves: if you calculate approximately, then twice the distance from the communication source will reduce the power of the radio waves by four times. As you can see, detecting such radio waves at a distance of several hundred light years from Earth will be a difficult task for space civilizations.
After all, as mentioned above, radio waves are not very effective for interstellar communication.
In addition, if Arecibo's message had come to us in 1913, we would not even have been able to receive it.
And here we come to the heart of the question: What kind of the interstellar message can be received by an alien civilization with technology comparable to humanity at the end of the nineteenth century (19th century)?