Yes, it means gone or over, but more than that as well. For example: "All his plans went out the window when he realized that his coin collection was worthless." It looks like there are some subtle differences between British and American usage: https://idioms.thefreedictionary.com/go+out+the+window This source says a way of thinking or behaving disappears suddenly and entirely.

The Oxford Learner's Dictionaries are an excellent resource. https://www.oxfordlearnersdictionaries.com/definition/english/window?q=window Idioms fly/go out (of) the window ​(informal) to stop existing; to disappear completely As soon as the kids arrived, order went out of the window.

I can’t think of anything that would “go out the window” other than “plans” or “dreams”. Usually used in the affirmative in the past. His plans to go to college went out the window when war broke out and he was drafted into the army. George’s plans to travel the world went out the window when his father died unexpectedly and he had to take over the family business.

Yes -- gone; completely and suddenly, with nothing remaining. It's a dramatic/emphatic expression. The phrase could be used in many different situations.

In the UK, we would say “go out OF the window” In the past tense, after the event, we would say “they have gone out of the window” Hope that helps