https://www.polygon.com/guides/2018/11/26/18112967/pokemon-lets-go-how-to-find-shiny-pokemon

Shiny Pokémon are like badges of honor for the hardcore player — a collection of the uniquely colored, rare monsters is highly coveted. What used to be a self-driven pursuit is now encouraged by the developers, with Pokémon: Let’s Go! having both an in-game item and a proven method to help capture shinies. And understandably, players are making the most of them.

The way to capture shiny Pokémon is streamlined for Let’s Go!, making it way easier than ever to seek out these special monsters. It will take a huge time investment, however, but one that’s actually … kind of fun if you’re into catching an obscene amount of Pokémon.