I was confused by how this is working for people so wanted to document it now that I have figured it out and ask for a feature request.
I have added a 4th axis controller for my U axis to my machine. I then updated to the new firmware which enables the U axis for the rotary.
From lightburn I can’t select anything but the Y axis (the other two radio buttons are greyed out). From lightburn though if I enable rotary and press frame I get movement in X/Y and nothing from U (as expected because lightburn is expecting Y axis to be driving the rotary).
But if I upload a job to the machine and turn on the rotary from the control pad the job will burn correctly. And I have full X/Y/Z/U control of the head / bed / rotary position at all times from the control pad. And the framing button works as expected (turns the rotary and moves in the X axis).
So if we could get the U axis enabled in the rotary setup along with any needed communication plumbing (if any) that would greatly simplify the workflow.