the smoke kinda looks like it's spelling "2001"
Linkyu
I would add, there are at least two other cases that necessitate Unity
the first is, unity is also used to make software, not just games. anything that has a 3d element can just be made in or with unity. I'm talking AR/VR stuff, builders, simulators, etc. I have a friend who made training software for welders in unity, for example.
the other one is vtubers. while not strictly necessary, the moment you want to model something a bit more complex you will likely have to deal with unity because the vrm format has become the standard (note: very over-simplified)
although they're not necessarily game cases, they're related enough that I wanted to bring them up
this is more prevalent in furry circles but not limited to there. when someone makes an original design for a species, they can decide whether to make it an open or closed species.
a closed species means that the creator forbids other people from creating characters from that species (though sometimes compliance rules are made instead). as you can guess, this is mostly unenforceable; some people respect those wishes, others don't. some will shun the latter, some others won't care.
btw I made it sound simple, but by god, the people of both sides often have very strong opinions about it
... fignificant other?