Adding fuel to the fire, the Duffer Brothers themselves admitted that they started production on Season 5 without a finished ending. They explained that because of tight production schedules, they had to start filming the early episodes while the later scripts were still being hashed out.
Source: https://www.pinkvilla.com/entertainment/hollywood/did-duffer-brothers-use-ai-to-write-stranger-things-finale-fans-furious-after-seeing-reddit-and-chatgpt-tabs-in-documentary-1399872
