What is this component in my microwave?
That's the waveguide cover. It's non-conductive, typically made of a mica/resin-based material.

Yours should be replaced. When you get that degree of carbonization (which should never happen, but eventually does, usually because food particles weren't cleaned off it promptly and left to attract electrical arcs on subsequent uses of the microwave), arcing becomes a lot more likely.

The arcing will eventually destroy the magnetron and possibly other components.

Fortunately, replacement waveguide covers are readily available. It can be a little tricky to get the old one out and put the new one in, depending on the microwave, but not at all beyond the usual household DIY-er. Yours appears to have a simple shape and be secured with screws, which should make replacement very simple.

You can either get a waveguide cover made explicitly for your make/model of microwave, or purchase a pack of sheets that can be used to cut one that fits your microwave. The former is more convenient, but of course costs somewhat more.