While alt-tabbing and minimizing the game my GPU reaches high load values (in Fullscreen and Windowed modes, thanks to @J_P)
This problem occurs while on the main menu:
and on all of the minigames too; Minigolf picture (same happens with the others):
Strangely this problem does not occur while playing on the Plaza:
I don’t know if it’s a known problem or if it’s just about optimization… after searching for similar topics it appears that nobody has ever reported such issue and I’ve decided to mention it just in case.