The Coffee Lake IGPU was broken since Sonoma and Sequoia. The symptom is booting up to a dimmed backlight. If put it to sleep then wake, it will come back with full brightness backlight or wait for about 3 minutes it will come back full brightness.
Thanks to hackintosh community, I found the fix here.
There are 2 things we need to do, the boot arg add -igfxblt and -igfxbrs, the igpu device properties add enable-backlight-registers-fix to 1 and enable-backlight-smoother to 1.
Reboot and it will fix the backlight problem.
