Launch Control XL 3 and Launch Control 3 use the macOS Core MIDI driver, so you do not need to download or install a driver to use them with a Mac. 

GarageBand uses the same Launch Control XL 3 and Launch Control 3 scripts as Logic Pro. Therefore, to set up your Launch Control in GarageBand, first you need to download the Logic Pro script installer from the link below, depending on your product:

Launch Control XL 3 Logic Script Integration Version 1.0

Launch Control 3 Logic Script Integration Version 1.0

Quit GarageBand, then run the script installer.

Once the installer is finished, connect Launch Control XL 3, ensure the firmware is up-to-date (Updating Launch Control XL 3 Firmware / Updating Launch Control 3 Firmware), and open GarageBand.

If you are prompted to automatically assign the controls, click Auto Assign.

If you do not click Auto Assign, or if the prompt does not appear, it can be enabled in GarageBand's Audio/MIDI settings by Selecting your Launch Control as the MIDI Controller.

GarageBand → Settings… → Audio/MIDI

Depending on the product you have, this will be:

• Launch Control XL 3 = Focusrite Novation - LCXL3 1
• Launch Control 3 = Focusrite Novation - LC3 1

GarageBand only allows the use of one MIDI Controller script at a time, but you can still use generic MIDI devices alongside the device using the script. For example, you could use the MIDI Controller script for Launch Control, and then use a MIDI keyboard for playing MIDI instruments. If you need to use multiple controller scripts, check out Logic Pro.

If you've completed the setup correctly, your Launch Control screen should read “GarageBand”, and the buttons and encoders should light up in DAW Mixer mode.

Additionally, when you press Mode to enter mode selection on Launch Control XL 3, Solo / Arm (DAW Control) and Mute / Select (DAW Mixer) should light up, indicating that the DAW modes are available. They will be lit dimly if another mode is selected, or brightly if a DAW mode is selected.

On Launch Control 3, Function should light up, indicating that the DAW modes are available.

If you don't see any of the above after completing these steps, see the GarageBand Troubleshooting steps below

Before proceeding with troubleshooting, ensure you have tried the GarageBand Setup steps above first.

If your Launch Control is not working as expected, check that GarageBand is up-to-date: How to manually update apps from the App Store - Apple Support.

If you continue to have issues in GarageBand with your Launch Control, try resetting the MIDI drivers in GarageBand's settings.

GarageBand → Settings… → Audio/MIDI

If you are having any general issues with GarageBand, refer to Apple's support resources: GarageBand - Official Apple Support.

As GarageBand shares a script with Logic Pro, you can refer to the Logic section of the Launch Control user guide for an outline of all the functions and controls available:

Controlling Logic Pro | Launch Control XL 3 User Guide

Controlling Logic Pro | Launch Control 3 User Guide

Launch Control 3's DAW Modes and Function Button in GarageBand

Once you've configured Launch Control 3 as described above, Launch Control 3 will default to DAW Mixer mode when you open GarageBand. Press the Function button to switch between the four Button Modes: Solo, Arm, Mute, and Select (the default mode).

In DAW Mixer mode, you can use the Page Up and Down buttons to switch between controlling Pan and Sends with the top row of encoders.

If you want to switch between DAW Mixer and DAW Control modes, press Mode, then press the Function button. Press Mode again to exit mode selection.

You can find additional guides for your Launch Control here:

Getting started with your Launch Control XL 3

Getting started with your Launch Control 3