Lenovo T99W175 / Foxconn SDX55 update on LVFS breaks FCC unlock

[Thilo-Alexander Ginkel]

Hi there,

Lenovo just published a new firmware for the T99W175 / Foxconn SDX55
5G modem on LVFS [1] that effectively soft-bricks the modem under
Linux as the FCC unlock no longer works.

I can boot up Windows and downgrade the firmware, but would be
interested in a more permanent fix.

What would be needed to figure out the new unlock procedure? Any hints
are much appreciated!

Thanks,
Thilo

[1] https://fwupd.org/lvfs/devices/com.lenovo.t99w175.firmware
[2] https://modemmanager.org/docs/modemmanager/fcc-unlock/#fcc-unlock-procedures-in-modemmanager--1184-1