I have a couple of projects I want to implement using an Arduino:

• a power switch to control an existing flat panel
• a temperature (only) reading sensor which measures the temperature of my focuser - again the hardware already exists, using 3 PT1000 platinum resistance thermometers, but it needs to be ingested by Ekos

The second of these can be connected directly by USB, but the first needs to use the UDP capability of the Arduino Uno R4, because it's fixed to the roll-off roof and I have no wired connection to that.
However, I'm failing at the first hurdle. I have been trying to get Indi-Arduino working on a directly connected USB environment in my office. I have tried lots of variants of the FirmataStandard.ino available in the repo, as well as the more-recent version in the Arduino IDE.
All of them fail to connect with my office computer (a Mac running Sonoma on Apple Silicon). Naturally I have ensured that the Arduino is not connected to the Arduino IDE at the same time (I've even gone so far as to restart the Mac before trying).
Is there something obvious I'm missing?

Thanks for any help!
Richard