Thanks for your reply!
Unfortunately after using WEG's SSDT PNLF, it' still the same And I have to change all 'GFX0' to 'IGPU' in the WEG's SSDT PNLF to make the brightness slider works again.
Here's my DSDT.aml, SSDT.aml, and SSDT PNLF.aml if you're curious. Oh and my laptop is MSi GP62MVR 7RFX
DSDT.aml
SSDT-PNLF.aml
ssdt.aml