I doubt that that is correct.
The kind of initiative shown by the OP is most likely encouraged by Purism. Of course from a Purism Support point of view, if you have a problem with cellular comms, they might ask you to restore the original modem and then reproduce the problem.
The fact that Purism hasn’t officially commented on this modem as an option more likely reflects the fact that they haven’t had the resources to test it out to their satisfaction and accommodate it in software and configuration if required, taking into account that any testing would doubtless require testing on multiple continents with multiple mobile network providers.
I believe that Purism is looking at other modem options and they may be looking at modems other than the one in this topic and/or they may be looking at this modem.
Edit: to add citation for previous para: T-Mobile 4G (!) shutdown beginning in 2026 - #5 by JCS (since @Privacy2 expressed concerns about “speculation”).