A mancave is different from a house.
Its a place where you fully invest in themes that bring you joy, versus value.
I could turn my entire home into 90s arcade style sports bar if i wanted to, But my girlfriend would leave me, any victors that come over will see me as childish, and the resale value will take a hit if i put urinals in all the bathrooms. and replace the fridge with a soda machine.
But a dedicated a room a nice place to expend that energy for your own satisfaction without it becoming a life hurdle. The garage, basement, attic, spareroom etc that you put your creative energy into is a man cave. a recreational space