I think people get mixed up a lot about what is fun and what is rewarding. These are two very different kinds of pleasure. You need to be able to tell them apart because if you don't have a balanced diet of both then it will fuck you up, and I mean that in a "known cause of persistent clinical depression" kind of way.
When people say they enjoy things, they usually mean one of two things. The first is that these things are fun; that is, they satisfy immediate emotional needs or desires for pleasure. Candy Crush is fun, for people who are into that sort of thing; waterslides are fun, watching TV is fun. Fun, in the way I'm defining it for this post, is the party food of pleasure; immediately and usually temporarily satisfying, and after that, mostly satisfying only as a happy memory (although some of these activities, like watching a TV show, can generate further opportunities for pleasure down the line like daydreaming, discussion, and making fanart). Like party food, this kind of fun is a good thing to have, and someone who doesn't get enough of it is at high risk of stress-related health concerns. Also burnout. A lack of fun is a major contributor to burnout.
The second kind of pleasure that most people talk about is rewarding activity. The lack of rewarding activity in one's life is a major contributor to depression. It creates a sense of purposelessness and worthlessness and generates a low attention span, sapping the ability to feel long-term motivation or pleasure. People usually try to pick themselves up with the first kind of fun, which is a band-aid but not a very sticky one; the lack of rewarding activity grows and festers over time. Rewarding pleasure involves working on something long-term that feels worthwhile. There are usually also spots of fun (or you wouldn't have gotten into the activity enough for it to become rewarding), but there also tends to be long slogs that aren't that fun. Nevertheless, when people report on doing said activity, they will speak about it with great enjoyment and remember it being enjoyable and claim they like it. (I like being a writer. Writing can sometimes be boring as shit.) (Look into Csíkszentmihályi's work on experience sampling and flow states for more info on this, it is FASCINATING.)
In Reality is Broken, Jane McGonigal sums up what she thinks are the most important contributing factors to rewarding activity. These are not the only factors, but I agree that they're a good baseline of the critical ones. I'm going to paraphrase them using different language. The four big contributors are:
Satisfying work. This is the vaguest one because different people find different things satisfying. Basically, the task itself should feel productive, and you should not feel bad about doing it to the point where it causes you distress. Satisfying work involves clear goals with actionable steps and a clear product, preferably something that you can see, touch or use. A clean house, a new high score, a freshly built table, a happy child.
Mastery. Rewarding pleasure is often something that you can get better at. There are things to learn, practice, improve. Improving your ability to solve tricky code problems, getting better at painting landscapes, figuring out fun new strategies in Magic: The Gathering, being able to build computers better or faster or cheaper. Mastery does not require becoming the best at something (although some people enjoy that specifically also), merely seeing progress in yourself and being able to take pride int he fact that you are better than you were.
Social connection. Rewarding pleasure often involves social or community connection. A long-term social group that discusses fan theories of their favourite show. Your weekly tabletop rpg. Teaching a room full of kids who to make leather belts. Working at a small bookshop and making small talk with all the tourists. Some people find social activity to be fun in the 'immediate pleasure' kind of way, some don't, but it is a critical factor in mental health and in the long-term... rewardingness (?)... of a hobby. Animals can also partially fill this niche, but be warned, they are far, far less effective than people. Your cat might be able to stop you from committing suicide today. You cat alone will not make your life satisfying.
Contribution. Humans are community animals and have a need to be something larger than ourselves or, more specifically to be of service to something larger than ourselves. Looking after kids, cooking big meals for others, creating art or physical products for others. Teaching the next generation how to read. Serving your God. Saving a species of small fish from extinction. Volunteering at your local charity shop or soup kitchen. Being a member of a crowd to reach the Guinness World Record for "most people fit into a storage crate". Making useful tutorial videos, being an entertainer, joining your local queer support group or political organisation. Humans fucking love to be part of something bigger than their own brain and they fucking love to help people.
The world is full of rewarding activities, and not all of them rate high in all four categories. The woman working in the charity shop warehouse and chatting with her coworkers isn't necessarily all that interested in mastery of her job (although I've worked in these places and some people do take pride in learning to be as efficient as possible), the musical hermit training to become the best violinist in the world might not be all that interested in social connection or how the audience actually feels about him. You might have noticed that I've listed hobbies, jobs, and non-employed but important life work (volunteering and childrearing) as possible rewarding activities; you can find rewarding activities everywhere. (In fact the lack of rewarding pleasure in our work lives is a very serious problem that companies keep trying to condescendingly band-aid over. The late David Graeber had a lot to say about this and I highly recommend his work, particularly Bullshit Jobs, which is a book specifically discussing the lack of above points 1 and 4 (satisfying work and sense of contribution) in so many modern workplaces and its distressing psychological ramifications). Rewarding activities are not 'fun' all the time; in fact, Csíkszentmihályi's work found that many of them are quite unfun most of the time. They do, however, create long term pleasure, and are emotionally and psychologically critical.
One final point: research shows that computer stuff counts less. This isn't a 'hurr durr edison was a witch get off your damn computers and get a real job' point; plenty of people do most of their rewarding activity on computers, because the supply cost is so low (most of us already own some kind of computer) and it's so much easier to find an existing community. But it does, psychologically speaking, count less; your brain isn't very good at seeing computers stuff as as 'real', on a primitive sensory level, as things you can touch with your hands or people that are right in front of you. Your massive community of fellow fans on the internet are less effective at filling your social needs than the crochet club at your local library, even if you like the people on the internet much more. It doesn't have to be everything, but ideally you should have at least one physical meatspace social club and at least one physical meatspace hobby, craft, or volunteer job. (They can be the same thing. You can volunteer at a soup kitchen for both.) They don't have to be the most important thing -- I care way more about my writing (electronic) than my crochet (meatspace) and I do the writing a lot more -- but the meatspace thing should exist, if you can manage it.
Ah. Should be less of a surprise then that ADHD (can't get started on stuff can't do stuff continuously disease) leads to depression I suppose. Or that chronic illness and disability do too.
