If a MIDI device is dimmed in Audio MIDI Setup on Mac
If a MIDI device is dimmed in the MIDI Studio window, the device may be turned off or disconnected.
Check if a MIDI device is turned on
In the Audio MIDI Setup app on your Mac, choose Window > Show MIDI Studio.
In the MIDI Studio window, double-click the dimmed device.
In the Properties window, verify that “Device is online” is selected.
If not, select the tickbox, then click Apply.
If the tickbox is selected, the device is turned on. Try reconnecting the device to your Mac.