science

So as I understand it most covid rapid tests test for the nucleocapsid protein. But the nucleocapsid protein is generally enveloped by the viral envelope in covid, as I understand it. How then are antibodies able to bind to, and covid rapid tests able to detect, this nucleocapsid protein if it's enveloped by the viral envelope? Would it not be better to test for the spike protein or something else on the viral envelope itself?

I don't understand that much about virology etc. but I was reading about this and now I'm going down a rabbit hole and hoping someone can clear this up for me.