Apple is moving away from device drivers in favour of Mac system extensions. Because Toolkit for macOS uses a device driver for RGB management, it will no longer support RGB customisation starting in June 2024.
Once removed, the RGB management feature will no longer be displayed on the home screen and there will be no way to customise RGB colours and patterns using a Mac. Your external drive's RGB settings will remain in the last saved state after the feature is removed from Toolkit. If you have access to a Windows PC, you can use Toolkit for Windows to change the drive's RGB settings. When you reconnect the drive to your Mac, it will use the new settings you just saved.