Thankfully, Ditto isn't an exclusive to one of either Pokemon Sword or Shield; you can catch the cute pink blob in both games. Unless you know exactly where to look however, it's unlikely you'll stumble upon it. That's because Ditto can be caught exclusively in the Lake of Outrage ...
The Wild Area has some of the best Pokemon in Sword & Shield. Here's where to find the best ones.
to choose, and all the old and new Pokétch Apps, plus how to get specific Pokémon such as Mew and Jirachi, Rilou and Lucario, Manaphy and Phione, Arceus, Eevee, Leafeon And Glaceon, Cresselia, Rotom, Ditto, Spiritomb, Heatran, Regigigas, and — of course — the mighty Feebas....