github.com/archagon/sensible-side-buttons

macOS mostly ignores the M4/M5 mouse buttons, commonly used for navigation. Third-party apps can bind them to ⌘+[ and ⌘+], but this only works in a small number of apps and feels janky. With this tool, your side buttons will simulate 3-finger swipes, allowing you to navigate almost any window with a history. As seen in the Logitech MX Master!

Extensive information on this tweak can be found here: http://sensible-side-buttons.archagon.net

To ensure SensibleSideButtons opens whenever you start your computer:

1. Go to System Preferences
2. Click Users & Groups
3. Click your username in the left panel
4. Click Login Items at the top
5. Click the plus button at the bottom
6. Go to wherever you put the app (probably your Applications folder) and double-click it