This doesn't solve the problem, but keep one of those freezer gel packs handy (not the ice ones, the small ones with the gel inside usedfor first aide). When your phone overheats, put a thin towel or a thin cloth around the cold gel pack and put your phone on top. The phone will remain dry and the cool gel pack will be pliable enough to provide a soft cushion--effectively chilling your phone quickly. At least it won't stay hot and you won't have to hold it by the air conditioner.
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.