Ignoring the fact that "funny" and "fun" are not synonyms, running is absolutely fun. It's type 2 fun, not the quick dopamine hit of watching a movie or playing a video game, but I absolutely love running and would definitely describe it as "fun".
Absolutely I do. And the process of training for it.
In '21 I was training for my first marathon before I got an injury and had to stop. In '22 I was better and trained for a marathon, where I felt amazing about achieving my goal time of 3:15. I also enjoy triathlons, which is part of why I'm not doing a marathon in '23 or '24, but right now I'm thinking I'll probably try for a 3:00 marathon in '25. The burn in your legs and lungs doesn't always feel great while you're running, but it doesn't take long afterwards before you absolutely love it.
Not everyone runs it in the shortest time possible. My longest run is probably close to a half marathon. It wasn't fast and it was fun. If it weren't fun, I wouldn't have done it.
That being said, some people who run it in the shortest time possible probably find it fun too.