Fun is you enjoy doing it. Playing video games and watching TV is fun.
Valuable is it makes money. Importantly, it's what other people are willing to pay you money for, not what you think is important or even good.
Meaningful is it's spiritually enriching. These are things you would regret not doing on your deathbed. Spending time with your family or going to church are common examples of things that are meaningful to people (and potentially fun). This one is defined based on one's internal compass and varies significantly from person to person.
You can come up with activities that are pure fun, value, or meaning. Measuring activities against these three axes has been a valuable mental model for my time management and life design.
There's jobs that are fun and meaningful, but don't pay much. This is like charity work or passion tax industries such as game dev, music, or art.
There's also jobs that are fun and valuable, but are meaningless. Working at a trading firm/hedge fund is a common example (though some people may find that it's all three or only one). Another example is being a successful startup founder working on the wrong problem.
Finally, there are jobs that are valuable and meaningful, but maybe not all that fun. To me, this is what being a startup founder (working on the right problems) or how I imagine a professional athlete is like.
The grand slam would be having all three, but in my experience these are exceptionally rare. If it's fun and meaningful, everyone wants to do it, and supply and demand pushes the value down. Most of these cases are due to unusual personalities that let one find fun or meaning in activities others don't. This ties into the common startup advice of paying attention to "founder-problem fit" and "what are your unfair advantages".