Well, to me this really does sound like the old Vive Input Utility is what's causing the issue here.
The fact that Quest 3 is showing Vive controller models suggests the package is falling back to the wrong controller profile after the OS/runtime update. Quest 2 may still work only because it is on the older runtime build. But the good thing is that I would not assume the app itself is broken. More likely the input mapping/device profile resolution changed in v2.3 on Quest 3.
For a quick test, log the actual device name and trigger axis values through Unity Input/InputSystem on Quest 3. If the raw trigger value is present but Vive Input Utility does not detect it, then the issue is definitely the third-party input layer.
Long term, I would migrate away from Vive Input Utility and use OpenXR/Meta input mappings. Short term, check if you can manually remap the Quest 3 controller profile or bypass that package just for trigger input.
