Yes, watching porn is haram in Islam and some other religions too.
In the 32nd verse of the chapter of Isra, Allah Almighty says, “Do not approach adultery!” he commands. Based on the “do not approach” command here, Islamic fiqh scholars have stated that any action that may lead a person to adultery is prohibited. We can also consider looking at obscene pictures or images within this category, so it is not permissible to look at such notions.

It is undeniable that it is difficult for young people to master their lustful feelings, especially in societies where sexual provocation and obscenity are an important commercial sector, and the natural sexual tendencies of young people are ruthlessly exploited. Increasingly abnormal and illegitimate means of satisfaction are spreading. For this reason, it is not permissible to make, sell, buy or watch things such as videos and games that will cause immorality in individuals and the emergence of sexual impulses.

In the Qur’an, men and women are ordered not to look at haram, keep their private parts well covered, and protect their chastity and honor (Nur, 30-31). Hz. The Prophet also stated that “…the adultery of the eyes is to look with lust…” (Bukhari, “Destiny,” 9; Muslim, “Nikah,” 44) and stated that it is not permissible to look at haram because it is one of the actions that lead to adultery. In this respect, men or women should avoid engaging in provocative behaviors and actions.

Watching erotic scenes negatively affects one’s spiritual life. Moreover, it can become a habit and a passion over time, causing some moral weaknesses and undesirable situations. For this reason, such a thing should be strictly avoided.

All sins and moral corruptions begin with an obscene look, develop with the insistence of the gaze, and then turn into actual sin. Moreover, the eyes take pictures of what they look at and store them in the archive of dreams. Wherever he goes, wherever he is, these pictures he takes are in front of his eyes in the realm of imagination.