There should be one screen each for self signing individual apps and it's updates, and another one for adding a public app store key to allow verifying apps and

There should be one screen each for self signing individual apps and it's updates, and another one for adding a public app store key to allow verifying apps and updates from that key. That would be factual and not scary. Yes, the question should be asked with the play store too. People should by default not trust a developer or store or OS for that matter that is scaring you into doing something.