Still also not how this works.

The phone will lower the wattage that it’s allowing „inside“ the battery. Either the charger does it or the phone will not charge anymore

So phone charges at 18w in the beginning wants to drop it down to 9w when almost full (80%). The charger either says „sure I can do that“ and provides the 9w or the charger doesn’t answer and the phone stops charging.

MFI is basically a seal of approval that it will 100% work as intended