To make Island your default browser on the macOS operating system, you can follow these steps:

1. Open the Apple menu by clicking on the Apple logo in the top-left corner of your screen.

2. Select "System Preferences" from the drop-down menu.

3. In the System Preferences window, click on "General."

4. Look for the "Default web browser" option and click on the current default browser (e.g., Safari).

5. A list of available web browsers will appear. Select "Island" from the list.

6. Close the System Preferences window.

After completing these steps, Island should be set as your default browser on your macOS operating system.