What is fun?

Can anyone relate? I feel like I don’t understand what fun is. I’m only ever comfortable or frustrated/annoyed, regulated or disregulated. I hate when I hear, ‘have fun’, what does that mean? Or ‘are you having fun?’ I don’t know, but the answer is probably no. On reflection it makes me feel sad. What is this fun? And I want to clarify I am not depressed or talking about depression. This has always been my experience. I hear about autistic joy and I’m keen to access this.