OP here:
Well, it's fixed. I finally got around to checking the 3 door switches, but unfortunately (I thought) they were all good. However I noticed the assembly that holds the switches didn't look quite right. The first photo was the assembly as it was when I opened the microwave and the second was with the tab hooked over the notch in the frame. That change moved the top switch 1mm, but IT WORKS! YAY.
It must have been a helluva bump going down the road to shift that tab (yes, we hit some pretty wicked ones) or it was installed that way in the factory in China and the plastic finally bent enough to move the assembly.
I never did find the main fuse, but I'm pretty sure it's good. :)
https://photos.app.goo.gl/qUuFosjxYADSUm166https://photos.app.goo.gl/Qo71Dv3ji1n6Wsqd9I don't know why the images don't show up so I put hyperlinks to them instead.