https://www.pcgamer.com/far-cry-5-secret-ending/

VIDEO: Far Cry 5's early secret ending, also available on YouTube

Just like Far Cry 4 gave you an early way out, Far Cry 5 also has a secret ending you can find within the first 10 minutes. In the opening scene, you head out with a federal marshal and the local sheriff to arrest Joseph Seed in the Eden’s Gate compound. Sheriff Whitehorse wants you, the rookie, to cuff him, and when given the opportunity you’ll need to comply by pressing a button.