The function takes a string input, keeps the uppercase letters, removes the lowercase letters, and returns the uppercase letters in reverse order.
[CODE]: 
def approximate_function(s: str) -> str:
    uppercase_letters = [c for c in s if c.isupper()]
    return ''.join(uppercase_letters[::-1]) 

# Test: PYTHON(approximate_function("AaBbCc")) should return "ACB"
# Test: PYTHON(approximate_function("HIJKLMNOPQRSTUVWXYZ")) should return "HIJKLMNOPZYXWVUTSRQ"