By greyed out, do you mean there isn’t an API key present in Jackett? I ask, because you’re supposed to enter the API listed in the grey area in Jackett into Sonarr. You aren’t supposed to enter any API key from Sonarr into Jackett as it sounds you are saying. You need to add them as custom Torznab indexers in Sonarr. Also, you need to click the add button and configure indexers before they will show up. There isn’t a list of preconfigured indexers that shows up when you run the program.
Sorry if I misunderstand what you’re saying. I’m not trying to offer juvenile advice. Your post just makes it sound like you are confused.