Iphone 11 pro max motherboard replacement cost

Anything board related usually means whole unit replacement, which is $399 plus tax for an iPhone 11 at an Apple Store in the United States and possibly a $6.95 shipping cost if it has to be shipped to you (not all stores have exact replacements in stock).

Yes, the motherboard of an iPhone can be fixed.

If to repair is more expensive than the device value, we would not recommend you to repair it unless you want to recover the data.