I just picked up the iPhone 13 Pro Max as well. Once I got it, I found I no longer could send messages to any Android users. Took it back and 30 some minutes later, I was told they had to reset the phone so that I could send / receive messages from Android users.
Now I have another issue:
My MacBook Pro, MacBook Air (brand new as of a month ago), and my iPad Air 2 - none of them will send messages to Android users. I have spent the last 3 hrs on my MacBook Pro on YT, reading forums, etc etc., trying to get just this one laptop to allow me to send/receive messages and NOTHING works. Beyond peeved that I paid this money for the 13 and getting this incredible headache.
Hoping that the new iOS system updates in the future fix this issue.