The hardest bugs don't crash. The program runs, and the answer is just wrong. Guessing and changing things at random wastes hours. Instead, work like a scientist:

Reproduce it with the smallest input that goes wrong.
Look inside: print the variables at each step, or trace them by hand.
Find the first moment a value differs from what you expected. The bug is just before it.
Fix one thing, then run your tests again.

Printing inside a loop is the quickest way to look inside:

def count_vowels(word):
    total = 0
    for ch in word:
        if ch in "aeiou":
            total = 1
        print(f"ch={ch!r} total={total}")
    return total

print(count_vowels("banana"))

The trace shows total never goes above 1: the line should be total += 1. (The !r in the f-string shows the value with quotes, which makes spaces and empty strings visible.)