Water spill on 2015 Macbook air screen

Many times liquid will never contact the Liquid sensors. You need to look for actual liquid residue and even corrosion on the components. Sometimes corrosion can be very hard to see even when using a magnifier. Both sides of the board must be examined. Even then, some liquid damage may only occur beneath a chip where many chips have solder contacts hidden beneath them. Since you have issues after using another built-in display, it means the Logic Board most likely has some sort of liquid damage. Sometimes it may be possible to remove small amounts of minor corrosion if it has not eaten into the metal or solder joints, but most liquid spills will require replacement of the board. If any connectors have liquid damage, then the board will need to be replaced.

Water damage is often extensive and ongoing due to corrosion. The computer needs to be inspected by an authorized service center. The computer is likely damaged beyond economical repair.