thanks so much!
After using dsdt then ACPI errors occured, I have to power off and restart. Then I boot without dsdt and with following arguments and settings, I can boot into Mojave( RX580 and UHD 630 acceleration fully supported):
-disablegfxfirmware (without it, I'll get errors: IGPU doing retry #1, 2, 3, 4, ......, 50, then panic and restart)
IntelGFX leaves empty
uncheck inject Intel
set ig-platform-id 0x3E920003
Send me Blueskovskys-iMac #2.zip