FOTA in external modem architecture.

Hello, I have been going through the DFU and FOTA lesson in the Nordic intermediate course.
I see that there is a FOTA support for a scenario in which we want to update a nrf90/91 device directly or support if we send the firmware update through Bluetooth or uart to a nrf52 for example.
But I don't see support for a scenario in which we have an external modem which is connected by uart to a ble device, nrf52 for example.
am I missing something?
thanks in advance,
Shlomo

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