The possible issue regarding updating is that the phone's XAA Csc code is a United States version, and you've now moved to Mexico.
Updates are sent out to a specific phone dependent on region and serial and build number which is probably why one phone has updated and the other hasn't yet
This can sometimes cause delays in updates and in some extreme cases stop updates but that's rare.
Was the phone purchased from a Network Store or was it purchased directly from Samsung in the States ?
I ask because that model of phone was sent the Samsung One Ui 3 and Android 11 in February 2021.
Try removing the sim card and insert another to see if that kick starts an update.
If all else fails you could look on the sammobile.com and xdadevelopers.com to see how you could go about manually updating the phone.
Using a Custom Rom / trying to use other methods to rollback firmware can bring about an unstable phone or it may not work properly if the process glitches or the wrong Rom is used. It may stop Samsung Pay from working if the procedure trips your Knox Counter.A person takes full responsibility if they perform this process and do so at their own informed decision. Again the process may trip Knox and may affect the Samsung Warranty. Samsung could levy a charge to put this right or deny support.
Or a Samsung Experience Store or Samsung Service Centre might be able to assist.
I wish you all the best with this.
Current Phone > Samsung Z Fold³ 5G.