Where does “室内遊戯” come from?

室内遊戯 (Japanese) comes from Japanese 遊戯, from Middle Chinese ゆうき.

室内遊戯 (Japanese): indoor game

Definitions

Step	Language	Word	Meaning
1	Japanese	遊戯	a game; a play; to play
2	Middle Chinese	ゆうき	—

室内遊戯 — Etymology, Origin & Word History | Etymology Explorer