Suddenly cracked 12 Pro Max bottom camera lens!!

Only thing you can do is show it to someone at Apple or one of their authorized repair locations but like already mentioned...they may not offer a repair. Too many factors can occur to cause it to happen so it may be impossible for them to deem it a defect on their end. A drop, something hitting up against it in a pocket (or purse or if you put it in your console in your car, etc etc), going between two extreme temperatures is even a possibility (although I don’t know how high the chances of it could be since I personally don’t line in a super cold environment). Not saying you did any of those or any of the other thousands of possible things that could be a culprit. Just pointing out the ways that it could be easy to question the cause.

Until/unless a recall is issued IF it ever happens it’s likely if they don’t choose to do a courtesy repair you would have to pay to repair it (if you have AppleCare+ it would help)...if that is the case and you pay to repair keep your receipt. If they later issue a recall and start offering to fix for people free of charge you can get a refund for what you paid. Not a comforting thought at the moment of course but it’s something to keep in mind. First things first though...get an appointment to have it looked at and go from there. Good luck!

Show the device to an authorized Apple repair location.

Do not be surprised if they offer no repair.