You can exchange. Still under warranty.
The challenge with that is from people's experience, mine included, Apple genius bar will push back.
I have stated my full story and all updates in this thread. Even when the senior adviser put a note in my case that the genius should replace my phone, I got a ton of push back. Even with all evidence in my case of everything I had done and sending files/logs to Apple, proof of calls with my carrier (AT&T), the genius still put it on me and told me there was nothing wrong with the phone and to take it up with AT&T.
He did begrudgingly replace my phone, but the replacement was no better. Even before leaving the store I waited to show the poor cellular performance and he still told me it was on the carrier and rushed me out of the store. Since then another Apple senior adviser had reached out to yet again collect more logs and files.
I do know that Apple has a 1 year warranty for manufacturing defects. The problem with that is proving or having Apple make a statement on the issue. Without that it's on YOU to try fighting with a genius about a replacement. We all know you're at a disadvantage when the genius plays the "well I can't tell what's going wrong, it's not the phone it's your service. we advise you take it up with them. bye".
The core problem that's been stated over and over again is that NO ONE KNOWS THE ROOT CAUSE. It could be hardware, software, a mix of both. It might be a bad batch of phones. It COULD be something with the carriers/modems which many of us are hoping can possibly be addressed with a software update. I am especially keen on hearing people's experience with the various betas which seem to continually update modem/carrier versions. Until we know the root cause of the issue OR until Apple makes a statement, then going to the genius bar can be frustratingly unhelpful.
Again it doesn't seem this is impacting all users/phones. Of course any phone can have issues with signal from time to time. However most of us posting about the issue have an idea of what service is like in our areas. I can say with certainty that over the past 10yrs of mobile phone usage in NYC, I have NEVER seen so many problems with phone service. Let's pare that down to just the past 2yrs with my previous iPhone 7+. In that time in all my normal routes and destinations I have never seen the problems I am experiencing with the Xs Max. Sure ANY phone can experience an issue, but having my phone struggle to maintain a data connection, send iMessages, load emails/websites, drop phone calls etc. in ALL the same locations/routes. That is a problem. Even anecdotally WITHOUT any evidence, a user would notice that.