Why is "pokaże" incorrect here?
pokaże is in future, he will show, he will have shown
why is it "pokazujesz czerwonego pomidora" but "chłopiec pokazuje nowy chleb" and not nowego chleba?
Unfortunately, there is no rule as to which foods are animate and which are not
Well, they are mostly fruits and vegetables, but true, there isn't any rule. I think it's quite likely though that this course doesn't teach any 'non-fruit-or-vegatable' noun that is considered animate despite not being animate in fact.