Yup! Ditto can transform into other Pokémon, and, so far, he's only being encountered in the wild in his transformed state. That means you can't see Ditto in Nearby or Sightings, and you won't know if he's spawned right next to you until you catch him.

Where can I find Ditto in 2021?

No, players cannot get a Ditto from eggs in Pokemon Go. The only way to find one is by catching a disguised one out in the wild.

Where does Ditto appear?

A Ditto will appear in the wild for everyone, and isn't just a common Pokémon that can transform at random - so if you catch one, other players nearby can get the same one too. It'll also appear as a result of a Lure or Incense.