nums = [1, 11, 5, 15, 6, 17, 3, 20]    # пробвай с nums = [1, 11, 5, 15, 6, 3, 20] -> няма да добави 3

new_list = []

for i in nums:
    if i <= 10:
        new_list.append(i)
        nums.remove(i)


print(new_list)