This is because according to a report from La Manzana Mordida, one of their readers order an iPhone 13 Pro along with the official leather case from Apple, but it was then discovered that the iPhone 13 Pro with its case does not sit flush on the MagSafe Duo, where the upper half is actually raised ever so slightly.
https://twitter.com/MKBHD/status/1441086122839339015
This is because of the larger camera bump which prevents the phone from sitting flat against the charger. Now the good news is that according to a quick test by MKBHD (see video above), it will work. While the phone does not fit perfectly, it will still activate MagSafe and will charge your phone, although we’re not sure if the lack of full contact could have any effect on charging speeds.
That being said, Apple did file a revised version of the MagSafe Duo with the FCC a few weeks ago, but the revised version was not launched alongside the new iPhones. Perhaps it could be coming at a later date, so for those who plan on getting the MagSafe Duo for their iPhone 13 models, either wait for an updated version or be careful when choosing which case to use with the handset.