Strictly speaking, a (Read-Only Memory) is a digital copy of a game cartridge’s data. A Pokémon Sword ROM would be an exact, 1:1 digital duplicate of the game card data extracted via a specialized tool (a cartridge dumper).
While the original Yuzu project was discontinued, several successors and alternatives have emerged as top choices for playing Pokémon titles: Pokemon Sword Shield Rom
Look into Pokémon TCG Live or Pokémon Showdown (competitive battle simulator), which are legal and free. Strictly speaking, a (Read-Only Memory) is a digital