In your concealed carry class, ideally part of it will be taught by an attorney skilled in criminal law.
He/she will know the difference between lawful and unlawful force.
And statutory (re the Illinois law referenced above), where you simply don't, or you're breaking the law, to the store owner who slaps up a sign. They can ask you to leave, and you must comply, but that's it, in Montana at least. But this varies considerably by state.
My sister recently went through this after a couple of dodgy encounters near Houston.
I told her to get whatever pistol felt good. She ended up with a Sig P365 (small hands), but you might choose something completely different.
But, it shouldn't be a .22, sorry. You're only going to fire if it's life or death. So, 9mm for most, and practice with anything, but carry the ammo the LEOs carry, Speer Gold Dot, Winchester Defender, whatever shoots best in your pistol. And never carry reloads.