I read here some time ago how to easily clean a very dirty microwave.

Put a large bowl of water in the micowave and heat on high for 4-6 minutes. Then let it sit with the door closed for 5 minutes. Then open up, remove the bowl of water and wipe it down with a cloth. The steam makes it clean easily. You can add lemon juice to the water before microwaving if you want a nice smell.

There are many ways, but to make it easier, put a cup of water or vinegar in the microwave in a microwave safe bowl or measuring cup and let it boil for a minute or two and create steam to loosen the nasty's. Carefully take the liquid out and wipe out the inside of the microwave, including the turntable and under it. If it is really nasty, get off what is loosened and repeat the liquid boiling in the microwave to loosen another layer. Once done, do a vinegar/water rinse to get rid of any bacteria or fungal spores that may be still be present. Leave the microwave open to make sure it dries completely before you close it. I hope this helps!

put a microwave safe cup with water in it. Give it like 4 mins on high to steam. Carefully remove the cup and wipe out

All you really need to do is put a measuring cup of water in the microwave for a minute or two so that you get a bit of steam. Then you can usually take a sponge it dish cloth and wipe it out.

Easy! Just place a cup of water in the microwave. Cook till the water boils. Do not open door. Let it sit for a good 5 minutes or so and let it steam. Now open up the door and give a spritz with full strength vinegar. All the gunk should just wipe right up!

The absolute easiest way is to clean it is to put a plain old cup of water in and cook for a few minutes until it starts to boil. Leave in the microwave to let the steam do its job and the water to cool off a bit. In about 10-15 minutes just wipe out with paper towels. You can also add a bit of lemon to the water.

naby options here...https://www.hometalk.com/categories/cleaning/appliances/microwaves