While the "Enqueue selected command" option is selected, the "Queue Name" option cannot be changed from its initial setting.
If the "Enqueue by name (Advanced)" option is selected instead, changes to the "Queue Name" option are saved.
EDIT: Actually, the "Queue Name" option can't be edited even when initially creating the action if the "Enqueue selected command" option is selected.
I started off using the "Enqueue by name (Advanced)" option, so I was able to enter a queue name.
EDIT: Fixed in v1.7.2.11