This page explains how to trade from Pokémon Legends: Arceus to Pokémon: Let's Go, Eevee!.
Trade Not Possible from Pokémon Legends: Arceus to Pokémon: Let's Go, Eevee!
Sorry, but it's not possible to trade from Pokémon Legends: Arceus to Pokémon: Let's Go, Eevee!.
Pokémon can't be traded from newer games to older ones.