You don't use XPath&CSS selectors at all (Except if you dont have choice). You rely on more generic stuff, e.g, "the button that has 'Sign in' on it":

    await page.getByRole('button', { name: 'Sign in' }).click();

See playwright locators: https://playwright.dev/docs/locators

Don't know about the poster, but I try to find divs and buttons in a fuzzy way. Usually via element text. Sometimes it mitigates changes, sometimes it doesn't. It's a guessing game. Especially when they start using shadow elements or iframes in the page. If I'm looking for something specific like a price or dimensions, I can sometimes get away with it by collecting dollar amounts or X x Y x Z from the raw text.