Pokémon Let’s Go Pikachu and Let’s Go Eevee mod: Alternate EXP Yield (75%) by Dio Vento (Included in Polished Pikachu / Enhanced Eevee)
This mod lowers the base EXP yield of every species in the game to 75% of its original value, allowing for a more natural level curve than the base game and preventing the drastic overlevelling that normally happens in Let’s Go.