There is no one answer to the question of whether or not Beethoven wrote his music for fun. Some believe that he did, and that he found great joy in the creative process. Others believe that Beethoven's music was more of a reflection of his own personal struggles, and that he used it as a way to express his emotions.
It is likely that the truth lies somewhere in between these two extremes. Beethoven was a complex and multifaceted individual, and his music reflects this. He was both a brilliant composer and a deeply emotional man, and his music is a reflection of both sides of his personality.
Ultimately, the answer to the question of whether or not Beethoven wrote his music for fun is up to each individual listener. There is no right or wrong answer, and each person will have their own unique perspective on the matter.