@ninja8tyu it depends on how semantic you want to get.
can you make a game without employing or commissioning anyone else? yeah definitely. for the vast majority of people though, they're still going to be relying on a lot of things that other people have made, and the extent of that just depends on how semantic you want to get.
a lot of games made by "solo devs" have someone else who made the music, or they have voice actors, or there is some art that was done by a third party. if you want to go even deeper, they didn't contribute to the engine they built the game in, or they're using plugins other people wrote for the engine. even testers could constitute as someone not being a solo dev.
i've made a game "on my own" before, called 3rogues. it still uses some plugins other people made and artwork i commissioned. when does a game go from being "solo dev" to SOLO DEV?
i think ZUN is a pretty good example of an actual solo dev. he makes all the art, music, and even the engine itself. few people have that sort of skill, let alone work ethic, though. people sometimes refer to toby fox as a solo dev, but he's not.
making your own engine i've tried using java, but i gave up because i couldn't figure out why making graphics were the way that they were
if true solo game dev: makes their own engine, music, art, coding...
then higher levels of solo game dev involve making their own os to run everything on it on, and making their own devices to run the os to run the game
@ninja8tyu there's also the point of like... how much of it constitutes a "game?" because a solo game dev could make a game that literally only uses text, it's been done plenty of times. but, an artist or musician couldn't make something considered a "game" just by using their art/music skills alone, they would need to incorporate some skills for game design or programming too. even the engine a game is made on can't really be called a game by itself, let alone the OS it runs on. so can you call someone a "solo game dev" if all they did was program the game and incorporate game design into it?
my personal definition is someone who did all the programming, art, music, and writing, but not necessarily the engine or any modifications to the engine like add-ons.
stuff like hangman, which is more to encourage word-finding and developing vocabularies
chess involved a board and its pieces
dnd is roleplay, and customization to how it works like its system and homebrew stuff could be considered mods for it
you lost The Game