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GO takes place in our world (or a true-to-life version of our world within the pokémon world) and Let's Go is in a related universe to that (start of Let's Go where you get sucked into the TV confirm this). As the multiverse is a thing, they've functionally connected the real world to the pokémon world meaning we're technically part of the pokémon universe, but with a very limited ability to interact with it.
