Make sure you unplugged USB, both cannot be connected at the same time.

Please check on the front panel menu, under Options. Interface mode should be set to Auto or TB. If it's forced to USB mode then Thunderbolt will not work.

Where you see Auto, you can change that to USB3, USB2 or TB. You have to disconnect the cable in order to change the mode.

You should then check in the Apple System Info app to see if the FF UFX+ is detected on the Thunderbolt bus.

Hi, I'm still in the fog.

I followed the routine I found here:
https://forum.rme-audio.de/viewtopic.php?id=31106
which seemed a reasonable solution but had no success.

I also switched the hardware front panel to Thunderbird.
No success either.

Any other advice?

Many thanks

Hi Matthias,
thank you for chiming in.

The driver is: driver_tb_mac_112

BUT:
I was checking the TB cable only on the interface as I realized you cannot go wrong plugging it on the wrong side. I thought the same was on the iMac side, I just double checked and seen that on the computer side the TB cable gets in even on the wrong side, which it was!
Shame on me and on Apple...
So, reversed the cable on the iMac and all runs fine.

Sorry for taking your time with such a stupid issue.

Wish you all the best and thanks for the amazing support, which is one of the many reasons why the UFX+ is my 6th RME soundcard.

Luca