This is just a quick post because I've seen some python beginners make some functions that are really in need of enumerate, but they don't know it ...
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Last line of your code:
new_arr = [letter for index,letter in test_letters if index % 2 == 0 and letter in vowels]
you forgot to actually use the enumerate function 😂😂
Wow! I can't believe I missed that. Fixed.