OK very interresting. I was just about to order a 2nd EyeTracker5 to go with my second monitor. I'm currently using my Tobii with Elite Dangerous on my primary Samsung G7. Was about to get another for use with my secondary Samsung G9 for sim racing with FaceTrackNoIR. GPU is nVidia 3080. If this is going to be a problem maybe I should find another solution.
For me the issue was having the plugin pack also installed. I uninstalled the lot, reinstalled facetracknoir and SetupFaceTrackNoIR_v203_Tobii5.exe and it works fine. If I install the Plugin pack it breaks it. This is entirely repeatable, I've checked. Give it a go and see if it works for you.
I've been wrestling with this for weeks with my Tobii 5 but have now fixed it! For me the issue was having the plugin pack also installed. I uninstalled the lot, reinstalled facetracknoir and SetupFaceTrackNoIR_v203_Tobii5.exe and it works fine. If I install the Plugin pack it breaks it. This is entirely repeatable, I've checked. Give it a go and see if it works for you.