Will the new chapter titles from Retitle give away the twists in my novel?

Not with the default setting. From version 1.9.24, in a fiction book the Retitle window has "No spoilers: a title never gives away a twist, a death or an ending", ticked from the start. The AI is then told never to reveal a twist, a death, a culprit, a secret or how the chapter ends in a title. Untick it only if you want titles that say plainly what happens. You can still edit any proposed title before you press "Rename".