Why is Ditto appearing everywhere in Pokémon Go?

gamepur.com:

Some unexpected things happen in Pokémon Go, primarily through some of the more unique events you can participate in throughout the game. However, most recently, multiple players have been finding Ditto appearing in their overworld, which is unusual. Typically, Ditto only appears when you attempt to catch a Pokémon, and you don’t know it’s a Ditto until you successfully catch it. Why is Ditto appearing everywhere in Pokémon Go?

Right now, we’re not too sure. There has been no official announcement from Niantic regarding the appearance of Ditto in the overworld, and it’s only happening in select regions. However, we’re guessing it has something to do with April 1, also known as April Fools’ Day. The appearance of this many Ditto could be because of this, but we’re not too sure. It’s likely tied to the Special Research event that has also appeared in select regions, namely the April Fools’ 2-Oh-22 Special Research.

It looks like you’ll have to wait until April 1 arrives in your local time zone, and it becomes midnight, according to other players reporting the event. We recommend catching as many Ditto as possible and seeing what Pokémon they become, with the chance of encountering a shiny Ditto.