If the ARC is connected to the computer you can assign rec and play buttons in Options -> ARC and Key commands in Totalmix -> ARC USB settings

This works only connected ta PC. You cannot connect the ARC USB and and USB drive at the same time on a UCX 2. On a UFX+/II/III, there is a separate USB port for the ARC USB and Durec.

In standalone on the UCX 2 you can only start/stop the recording in the menu on the device.

To clarify, I have a USB stick in back of fireface. Will be plugging ARC into Mac USB.

So I've got the ARC plugged in. Everything seems to be working fine, however, I assigned the 'Record/Play Stop' to a button but it's not working.
To be clear, I’d like to be able to start the recording and stop it as well, with the same button (if possible).
Tried the ‘Record Start’ but that only starts recording. Is there a way to record start and stop with one button?

Do I understand well that the ARC USB configuration is only possible for in not-standalone mode, and that the configuration is fixed when in standalone mode? That's with a UFX III (waiting for it to arrive here).

I was so far assuming the UFX III could save the ARC configuration as it does for the state of Totalmix.

If that's accurate, any hope it may be changed some day?

My use case is replacing my monitor controller (or getting rid of it) and a feature that I'd miss is muting the output... I was thinking on the Arc to map a button to a Mute group for the Main, Speaker B, Phones 1 and 2...