Flatten Track Stack for Selected Channel Strips
Removes the tracks from the track stack, and remove the stack channel strip from the mixer. NB that when you remove a stack the channel strip _moves_ to the normal location for an AUX channel or a VCA.
I assume that there is a separate command for this when working in the mixer since there really aren’t any tracks to work with.
In the standard configuration of Logic Pro X the ‘Flatten Stack – ⇧⌘U’ command has no overloaded commands, so you could assign the same keyboard sequence to the ‘Flatten Track Stack for Selected Channel Strips’. I have done this and don’t see any particular downside. The same can be true for ‘Create Track Stack for Selected Channel Strips — ⇧⌘D’.