iPhone 12 Pro Max poor reception

That's an incorrect assumption that runs counter to the experiences of many.

For many of us, it has the best reception of any iPhone ever released, and any reception issues have been fixed for a growing number by a cellular carrier settings update.

Update your carrier settings on your iPhone or iPad - Apple Support

You are correct, there are several people having issues, but it is not correct to assume this has anything to do with reception per se, every indication is it has to do with antenna configuration at the cell tower, or else it would not be fixable via a carrier settings update.