Is it possible to extract the firmware of an Arduino BLE or IoT board wirelessly?
Technically, the firmware can read its own application section, but it won't send it to you wirelessly (or via any interface) if such a feature isn't implemented in that firmware. If you were to implement the firmware yourself, you can do (almost) anything. But if it is a third party firmware, this will not be possible.
The reason this works with arduinos and avrdude is, because firmware up- and download are implemented in hardware (ISP, works without a bootloader).