To encounter these Pokémon in a Max Raid Battle, you'll need to connect your Nintendo Switch system to the internet through the Y-Comm or by selecting Mystery Gift in the X menu, then selecting Get the Wild Area News. After that, whenever you see a pillar of light shining from a Pokémon Den in the Wild Area, you can walk up to the Pokémon Den and interact with it to start a Max Raid Battle. This event does not affect the Pokémon encountered within Dynamax Adventures.
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Encounter Eevee and Its Evolutions in Max Raid Battles | Pokemon.com
You’ll find the Evolution Pokémon and friends in Pokémon Sword and Pokémon Shield, and you might encounter a Gigantamax Eevee or a Shiny Eevee.www.pokemon.com