I just played 40 minutes Mario Kart in dock mode and when I wanted to take the switch then in handheld mode, I felt that my switch is a bit warm behind. Is that normal?
Yes, that's normal.
Yes, actually. But if it gets too hot, you should feel the ventilation somewhere on the edge, otherwise there's something broken.
Yes, that's normal. PS4, XBOX, PC, etc. Weden, too, warm.