It is normal for the outer shell of the microwave oven to be very hot after use.
There are two larger heating elements in an ordinary microwave oven: a magnetron and a transformer.
They are generally fixed on the right side of the microwave oven (viewed from the front), with the magnetron at the top and the transformer at the bottom. Therefore, after the microwave oven has been operated for a long time, the shell near the right side (front half) will be relatively hot. This is normal. Moreover, there are heat dissipation holes on the left side or the upper left top of the microwave oven. Steam often overflows from these parts and the temperature is higher.
If the microwave oven is a grill type, check whether it is set to combination mode by mistake, so that the temperature of the top surface of the shell will be relatively high.
This depends on the length of time you use it. If the continuous high temperature, such as barbecue, exceeds the limit temperature, it will automatically protect and naturally cannot work. This is normal.
If you use the light wave combination function, this situation will not easily occur because it works alternately. If it is like this for a short time, it means that there is a fault in the internal circuit, especially the high temperature protection caused by poor performance of the magnetron and high-voltage transformer.