The same for me... The 'Unknown CPU' in About this Mac dialog doesn't bother me because the system is rock solid (i5-8600K), sleep works nicely and the performance is great in benchmarks and real world applications, too. Also the CPU frequency goes between ~1 - 4.3GHz dinamically, so power management is working - checked in Intel Power Gadget app.
Strange, because I see others got their 8th gen. i3 CPU identified by High Sierra with the very same motherboard & BIOS version, and with the same Clover config that I'm using. What causes this 'Unknown CPU', somebody knows?
With the UHD 630 I have no luck, it's definitely not native, macOS cannot even load with using the iGPU only.