I have just had a series of extremely frustrating interactions with Apple support over the last 1.5+ hrs about a similar problem with my iPhone 11. One of the lenses shattered last week without any apparent cause. I happened to glance over at it while I was having a conversation with someone and saw streaks across the lens. My immediate reaction was "How in the world could I have scratched this lens and only this lens with another one just millimeters away?" Turns out it wasn't scratched... it was shattered. There is not a single scratch, scuff or dent on the lens bezel, the adjacent lens / beset, or the LED light. I keep the phone in a rubber case with a strong screen protector and had not dropped the phone or mishandled it in anyway. Even if I had dropped it, I would probably have a better chance of winning the lottery tomorrow than dropping this phone in just such a way (and just the right amount of pressure) that the actual camera underneath is not damaged, only one lens shatters AND nothing else receives even the smallest scratch or ding. -- Like yours, mine is still under warranty. HOWEVER, since it is my business phone, I also bought AppleCare with it as an insurance policy. It turns out that AppleCare doesn't add that much value in this case as you've only paid for the privilege of being able to pay ADDITIONAL $$ over and above the cost of AppleCare to have (what is clearly a manufacturing / design defect) repaired within what would normally be considered reasonable expectations.
It is extremely disappointing to have wasted multiple hours of my day trying to resolve this simple issue but still come up empty handed. I've invested ridiculous amounts money recently and over the years in Apple products. I did that happily because I never really experienced a lot of problems with their products and, IF I did, it was always a relatively quick / simple / reasonable resolution process that I'd leave feeling positive and "whole". That has certainly not been the case today or anytime over about the last 1-2 years.