The Isle of Armor Pokédex glitch occurs in Pokémon Sword and Shield. Pokémon from past generations previously unavailable but made available with the Isle of Armor expansion will not register in the Pokédex if transferred from Pokémon Home. However, there is a workaround to register it in the Pokédex even if it was transferred from Pokémon Home, namely taking the Pokémon in and out of Day Care, which will register the Pokémon.