Mine is overheating a couple minutes into a game. Played same game on my Note 8, no problems there. One day with my Note 9 and I'm experiencing issues already. I've also owned Note 4, 2, 1. No problems until the 9...
How did you revolve the overheating issue?
Did Samsung hook you up with a third party company?
It seems I'm having the same issue as you did. My Note9 gets really warm in the idle state and the battery drains fast.
When I contacted Samsung about this issue, they hooked me up with UBREAKIFIX.