Question: how to tell the difference between a male and female eevee?
Answer: Unlike other Eevee, in Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!, the partner Eevee has gender differences. Male partner Eevee look the same as all other Eevee, but female partner Eevee have a unique heart-shaped tail pattern. In Generation VIII, this gender difference was applied to all female Eevee.