Best answer: Pokémon Unite is set to come to Android and iOS in September 2021, but The Pokémon Company hasn't announced a specific day of the month yet. It's also coming to Nintendo Switch in July 2021.
What is Pokémon Unite?
Eschewing the usual Pokémon formula, Pokémon Unite is a MOBA (multiplayer online battle arena) that takes place on Aeos Island. It's here that players will compete in 5v5 battles and score points against their opponents to win matches. Players will earn these points by defeating rival Pokémon and depositing the Aeos energy they earn in the opposing player's goal zones. Players will be able to catch wild Pokémon, level up, and evolve their Pokémon.
When does Pokémon Unite release on Android?
The Pokémon Company has only stated that players can expect Pokémon Unite to launch on Android and iOS sometime in September 2021. It has not provided an exact date, so this could be subject to change.
When does Pokémon Unite release on Nintendo Switch?
Pokémon Unite is actually expected to hit Nintendo Switch a few months earlier than its mobile counterpart in July 2021. Again, there isn't an exact date, but given that it's currently July we should be learning of one very soon unless it gets delayed.
Does Pokémon Unite support cross-play?
Pokémon Unite will support cross-play between Android, iOS, and Nintendo Switch. This is a special case where all parties involved felt it would be best for players if cross-play was enabled. This shouldn't be taken as precedent for future Nintendo titles, however.