Mobile heating while charging, back ground apps running tym also mob get over heated.
Can you first tell me the device firmware/software version.
Go to setting => About => Software information.
Next, if you are using ROG inbox supplied charger which is a 30W fast charger the lite heat is quite normal.
Also, can you let us know the ambient room temperature around u? Also is the heat way you much or its bearable? During lite work the heat shouldn't be that noticeable.