I think fix is a stretch and this started as a joke because the box was basically useless after 30 minutes since the remote would be unresponsive. Had this sitting in my basement for 6 months doing nothing until a FireTV Stick 4K died in our guest room.
I popped it out of the case, and just put little stand offs all the way around. Then put it between the shell to keep it off the TV stand and from anyone touching hot parts.
Hilarious to me but totally solved the overheating with passive cooling.
There must be dozens of thousands of Onn players like this in the wild, plus about a dozen more devices all using the same SEI Robotics design, including Google's own ADT-3.
If there was any overheating issue, we would know.