How can I improve my gallows game code?

Displaying the word on screen

First, let's make the function that displays the word on the screen, along with the underscores in the letters that should not be displayed. For this we can do:

def exibir(palavra, tentativas):
    caracteres = (letra if letra in tentativas else '_' for letra in palavra)
    return ' '.join(caracteres)

This will display the word, except for characters that are not in tentativas, which will be replaced by an underscore, _.

exibir('woss', [])  # _ _ _ _
exibir('woss', ['s'])  # _ _ s s
exibir('woss', ['s', 'w'])  # w _ s s
exibir('woss', ['s', 'w', 'o'])  # w o s s

Drawing the word

The draw part which will be the word you did well and did not have the what to change:

from random import choice

palavras = ['chiclete', 'arroz', 'banana', 'feijao', 'nutella']
palavra = choice(palavras)

Game logic

We start by defining the amount of user errors and the attempts he made:

tentativas = set()
erros = 0

At this point, I used tentativas as a set, since it will not make sense to have duplicate attempts and the set has optimizations in its access and search relative to the list. At this point it is almost like a micro-optimization, but it is the tip for you to study.

• How can the search for an element in a set be the(1)?

For the loop, you don't have to create a variable just to be true always, you can directly use the True. Just as you do not need to print the "word" outside the loop, do it only inside it and do it only once.

while True:
    print('A palavra atual é:', exibir(palavra, tentativas))

    while True:
        tentativa = input('Digite uma letra ou palavra: ').lower()
        if tentativa not in tentativas:
            tentativas.add(tentativa)
            break
        print('Você já fez essa tentativa.')

See that I used the lower method of string to convert the user input to lowercase always, so we don't have to worry about it and I used another infinite loop to check the input from the user, this prevents you from having to do the same input twice in code.

At this point, we can already check whether the user won or not. This will occur when the word no longer has the character _ or when the user enters the entire word correctly:

if '_' not in exibir(palavra, tentativas) or tentativa == palavra:
    print('Você venceu')
    break

But if the user did not win, we must check if he at least hit a letter or made a mistake, to then account for the errors.

if tentativa not in palavra:
    print(f'Você errou! Só te restam {5-erros} tentativas')
    erros += 1

And finally end the game when the user reach the six unsuccessful attempts.

if erros == 6:
    print('Você perdeu!')
    break

It would be more or less like that...

from random import choice

def exibir(palavra, tentativas):
    caracteres = (letra if letra in tentativas else '_' for letra in palavra)
    return ' '.join(caracteres)

palavras = ['chiclete', 'arroz', 'banana', 'feijao', 'nutella']
palavra = choice(palavras)

tentativas = set()
erros = 0

while True:
    print('A palavra atual é:', exibir(palavra, tentativas))

    while True:
        tentativa = input('Digite uma letra ou palavra: ').lower()
        if tentativa not in tentativas:
            tentativas.add(tentativa)
            break
        print('Você já fez essa tentativa.')

    if '_' not in exibir(palavra, tentativas) or tentativa == palavra:
        print('Você venceu')
        break

    if tentativa not in palavra:
        print(f'Você errou! Só te restam {5-erros} tentativas')
        erros += 1

    if erros == 6:
        print('Você perdeu!')
        break

^{see working on Repl.it}

Not as smaller as its version, but considerably simpler and more readable.

As for using f-string to format a string instead of the % operator, read:

• what to use to format a string, % or format?
• how to do string interpolation in Python?