As others are saying, you can and likely should include these as activities, assuming they involved a decent amount of your time.
I’ll just add there is a real art to describing such activities in a way that will be interesting to bored admissions officers slogging through 50-100 applications a day.
There is a widespread temptation to try to make them sound “impressive” in a business-resume sense. Everyone does that and I think AOs are consistent in saying that doesn’t really help distinguish applicants.
But really strong, specific, fun descriptions–THAT can wake them up a bit and cause them to smile.
So I have no idea what you did, but I would ask yourself questions like what would you actually say to a gamer if you were trying to entice them to play one of your games? Indeed, what do you love as a gamer, and how were you trying to do something you would love? You shouldn’t use jargon, but there is no problem using the specific verbs, adjectives, and so on common to the activity.
So, a surfer should refer not to “challenging waves” but to “gnarly waves”, because that creates a strong, specific, fun image. There have to be equivalents of “gnarly” you can use to describe the challenges in your games (or, for that matter, maybe you can use gnarly!), instead of bland words like challenges.
And sure, in an ideal world you could say you created a gnarly game that was played by 1.2 million people (specific numbers grab attention too). But you shouldn’t be overly concerned about what you can’t say. Just focus on making the most of what you can say.
If you do that, you will not only be explaining how you used your time, you will be coming across as a truly interesting person. Which is always a good idea.