What is the ruling on suppressing a wet dream during sleep, what are its harms, and is it a disease that requires treatment? Also, what is the ruling on the fluid that is discharged when looking at something stimulating without desire?

There is no evidence that prohibits grasping the organ to prevent the exit of semen, unless it is for pleasure. It is better to avoid it to prevent harm. If the male organ is grasped and semen does not exit, then ghusl (ritual bath) is not required of the person, whether awake or asleep. Ghusl is only obligatory upon the exit of semen, and some say it is obligatory upon the movement of semen. There is no sin upon you in the case of sleep, as the Prophet, peace and blessings be upon him, said: "The pen has been lifted from three... and from the sleeper until he awakens." The white fluid that appears is likely madhy (pre-seminal fluid), which is impure and necessitates washing whatever it touches on the body and performing wudu (ablution). As for what touches clothes, there is a difference of opinion; the majority say it must be washed, while some suffice with sprinkling water on it.