The big issue is that there is no consensus on "fun". You could make a "fun" platformer but you're not converting people who don't like paltformers (even if they make a few exceptions like Mario or Celeste. You're probably not making the next Mario, though). If the game is boring to that audience the solution shouldn't be to change genre. Not unless your goal is to attract a general audience.

So "the game isn't fun" needs a lot more context on who is saying it, and is useless otherwise. Do they like your genre? Are they miscommunicating what sounds like a game design issue when it could be an art/sound issue? Did they just grab your game in a bundle/gamepass and weren't really in the mood to play your game?

It's all speculation. And it's probably better to find better feedback than try to psycho-analyze every comment that way.