Post the first few pages of FAH's log. Since most of us (including me) don't have a laptop with Optimum technology, we have to depend on you to answer your own questions.
Your NVidia or AMD GPU will be detected by FAH (if you've installed the right drivers) and the Intel iGPU will not be detected since it's not supported -- so you can neither select it or deselct it.
From what I understand, the OS makes a selection of which GPU is treated as primary and changes that selection based on whether the video activity is minimal (such as displaying the desktop) or maximum (such as playing a game). I have no idea if FAH is recognized as gaming and whether the client is smart enough to report you want an assignment for you NV/AMD GPU even if you're currently running on the Intel and whether it's smart enough to instantly switch to gaming mode.
If this doesn't match your observations, let me know.
GPU of Intel NUC Hades Canyon isn't working
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