Pokémon Let’s Go Pikachu and Let’s Go Eevee mod: Harder Trainers by Dio Vento (Included in Polished Pikachu / Enhanced Eevee)
This mod increases the challenge of bosses and Coach Trainers as well as making some other minor Trainer changes.
Currently edits 124 Trainers.
Put the Atmosphere folder on the root of your SD and then boot the game normally while running Atmosphere CFW, the mod should load silently and seamlessly.