I have an LG brand microwave and when it turns on it turns on and when I want to heat some food, sparks come out of the door from the inside and it starts to smell like burning. I even removed the mica that protects and prevents dirt from entering the magnetron and continues to burn.

if it continues to sparks then most likely the magnet antenna is damaged you have to check that

The metal housing acts as a shield, and is the neutral connection and this, or should be grounded. You have to put the mica back. And you should check that you do not have the electrostatic paint skipped, if so, the energy of the micro goes through the peeling generating arcs and overloading the magnetron., Be careful you can burn it or maybe you found the diode discharge. Check the condenser, a short capacitor can produce arcs.