The 12 Pro Max has an OLED screen so there's no backlight. Not sure exactly what a white screen means in this case.
Is the original screen even partially functional? Can you confirm a picture appears with it reinstalled?
But yes, it is entirely possible for the screen to be non- or partially functional even with no visible damage; happens all the time, actually. If you get any kind of picture with the broken screen, then chances are the new screen isn't working and you'll need to contact the seller for a replacement.
Otherwise carefully check the connectors going to the display for any bent or broken pins; use a magnifying glass and a bright light for best results. Clean both sides with 90% or higher concentration isopropyl (rubbing) alcohol, reassemble and test.
Let us know what you find and we can go from there.