Pokemon Let's Go (opens in new tab) Eevee and Pikachu made catching shinies easier and more intuitive, but you can't get much easier than the new Pokemon Pass app. As The Pokemon Company explained (opens in new tab), app owners can obtain a shiny Eevee or Pikachu simply by visiting a US Target store between May 11 and June 23.
You can download the app for free via the iPhone App Store or Android Google Play store. Once you sign in - using a Pokemon Trainer Club account, which is also free - all you need to do is wait for the event to start on Saturday, May 11. Once it begins, just visit your local Target - again, provided you live in the US - and "the app will then guide you through several prompts, including one to scan a special QR Code found in-store, so you can claim your Shiny Pikachu or Shiny Eevee."
If you own Let's Go Eevee, you'll receive a shiny Pikachu, and vice-versa. Both Pokemon are level ten, and they come with some pretty good moves, too. The Pikachu has Thunderbolt, Double Kick, Double Team, and Thunder. The shiny Eevee comes with Double-Edge, Iron Tail, Helping Hand, and Facade. Incidentally, I still love the mental image of Eevee using Iron Tail - just a fluffy metal mallet to the face.
The Pokemon Pass app also comes with a few photo stickers from the upcoming movie Pokemon Detective Pikachu, but that's about it for the time being. It's pretty barebones, so it'd be cool to see it fleshed out with some Pokemon Sword and Shield (opens in new tab) stuff in the future. If nothing else, it'd make it a more compelling download.
For your non-Target-related shiny escapades, here's how to catch a shiny in Pokemon Let's Go (opens in new tab).