I've just checked this issue again, it is still present in Unity 2022.3.5f1 & Input System 1.6.3.

I already had 'Both' Input systems enabled. Only by switching to the Old input system could I then connect to Phidgets. I also found a post about this issue on the Unity forum from a few years ago. https://forum.unity_com/threads/new-input-system-possible-to-prevent-device-from-being-recognized-or-r...

I've just discovered this issue now, using Unity 2021.3.15f1 and the New Input System v1.4.4. Did you manage to find a solution / fix for this?