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The more likely Eeveelution is EEVEE Evolving using a Nintendo Switch exclusive Method: The JoyCons!
There is “Soaring” using JoyCons and Eevee evolving in mid-air!
Training your Eevee in a “actual training camp/gym” like Stadium and Eevee Evolves to fighting-type. Training requires JoyCon movement.
Steel-type Eevee: Simply grabbing your Eevee from Ultra Sun Moon and trading it to Nintendo Switch using PokéBank on the Switch.
and unlikely but a possibility: Ultra Space returning. Actually Evolving Eeeve while soaring inside the “ultra space.”
