Not sure how many correct is needed for the certificate, but I do this just for the experience.
Not sure it is legal to put code here, but since it is a wrong answer, it couldn't hurt.
Row[Map[Column[{ToUpperCase[#], ToLowerCase[ #]}, Frame -> True,
Background -> RandomColor[]] &, Alphabet[]]]
This is even more efficient, since Alphabet is already lower case:
Row[Map[Column[{ToUpperCase[#], #}, Frame -> True,
Background -> RandomColor[]] &, Alphabet[]]]
One more thing: I am using 12.1(desktop macOS), and we know that at least some of the quizzes were made with 11.3. There may be some subtle differences -- the developers have been working on updating the parser, for example -- that may create some differences in the code.