To dispose of an old microwave you can scrap it out by taking it apart and then selling the copper, transformer etc out of it.
Then you can scrap the rest of the microwave as tin.
However you would need a lot of tin to make it worth the trip to the scrap yard.
But if you just want to dispose of it the scrap yard will likely take it as is for scrap even for nothing.
Or you could sit the old microwave out at curbside for scrap metal people to pick up.
In some locations people go around looking for scrap metal and will pick up the scrap metal you put out including the microwave.
You can do the same with other appliances.
For me I have a spot to put stuff like that and I also pick up some scrap when I see it and add to my pile.
Then when the price is high enough like now and I have enough scrap metal I take the load of scrap metal into the scrap yard to sell.
A local recycling center around you may also take it as well but if you have a scrap yard and are close by you can drop it off there as well.