This article demonstrates how to load Arcade in GarageBand:
Open a GarageBand project
Go to Track from the GarageBand menu and select New Track, or click + on the left-hand side above the track headers.
Select the Software Instrument option on the left-hand side and click Create
Turn on Smart Controls
in the top left control bar. This will open the Smart Controls window at the bottom of GarageBand if it is not already open.
In the GIF below, Smart Controls are already open.
In the Plug-ins section of the Smart Controls window click on the dropdown menu. GarageBand automatically has the * Classic Electric Piano selected by default
Click the up / down arrows to open the menu, not the plugin name
Navigate to AU Instruments > Output > Arcade and click Stereo to load ARCADE
Apple's GarageBand manual further details this process. If you need additional help loading Arcade in GarageBand, reach out to our support team and we'll be happy to help further!