it says the current temperature is 72 degrees celcius, which is a normal operating temperature during gaming. the tjunction temperature is the temperature the gpu will prevent the generation of more heat, so it can cool down
i had that problem with my tablet. i used to charge it overnight, which didn't turn out to be healthy. try to charge your phone during the day with the included charger. charge it when you are below 25% and stop charging aroung 90%. it really helps the battery keep at it for a longer period of time.
if you have an intel cpu or and amd apu, then you can connect the monitor to your motherboard to see if the problem is your gpu. you could also just try swapping out the gpu with a different one, if you have a second one laying arounde