According to XTU requirements:
The Core i7-8550u is not a Desktop, HEDT or high-end Mobile processor.
Perhaps the Intel Customer Support engineers can get us an explanation from the XTU team's Marketing folks. I fear that the answer that they get will only be repeatable under NDA, however.
My personal opinion (in addition to my general dislike for this tool) is that XTU is not the right tool to support this usage model. This capability (amongst others currently implemented in XTU where they never belonged) needs to be implemented in the BIOS. Why? Because it is responsible for the implementation of most of the processor initialization and the implementation of all power and thermal management (both the initialization and programming of all active cooling (fan speed control) solutions and the implementation of all (mostly ACPI-based) passive cooling and power management strategies). Yes, this does place a burden on the motherboard (and laptop) manufacturers and yes, this could result in inconsistent implementations. Perhaps Intel needs to implement a backbone for this capability that the IBVs could integrate (or develop their own custom replacement for, since they are the kings of NIH). The BIOS developers for the various board and laptop manufacturers could then differentiate themselves with the Setup GUI that they provide on top.