Top one is actually quite good. If it were for real, I would write it as a proper named function. That way is real nice for avoiding duplication, and something I didn't think of.

def is_palindrome(s: str):
    processed_text = ''.join(c for c in s.upper() is c.isalpha())
    return (lambda x: x == x[::-1])(processed_text)

100% cursed. Love it.

24 characters shorter, and I respected proper formatting rules (still a joke solution though).

nice!

This works. Better to save the computation to a variable so you don't have to perform it twice. You can do this without regular expressions as well, which (in this simple case) is probably better.

tbh it looks mid