A Nintendo Direct has aired and featured some Pokémon news. After a short recap of earlier info, it's revealed that at night trainers come out to battle in a tournament called the Z-A Royale
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In special zones, similar to wild zones but marked in red, if a trainer sees you they will challenge you to battle. You can also sneak up on a trainer or their Pokémon, similar to taking wild Pokémon by surprise in Legends: Arceus. In the tournament, trainers start at rank Z and work up to rank A.
Here is the Pokémon part of the Direct: