The Chinese government, while not openly supporting Russia, has been repeatedly accused of covertly doing so. Imagine what kind of harm a device used for reconnaissance could do if it secretly works for the other side.
https://cybernews.com/resources/how-to-access-google-play-ap...
They likely flash verified firmware and use a verified app version, not the latest one from DJI's website... Maybe they have their own code, by now. Especially with reconnaissance drones. The Ukrainians probably need to do this, not just because of the obvious possibility of a "backdoor", but RF adaptability in the EM warfare situation.
I would worry more about contractor John Doe bringing a compromised private phone to a government or industrial facility. Not sure a highres video feed from a drone could be easily exfiltrated unnoticed, anyway, since they usually don't come with WWAN hardware built-in. But the phone itself would be able do all sorts of reconnaissance and become an attack vector in a sensitive context. Then again, this is not specific to drone (software), but all untrusted software people install.
Otherwise, it might depend whose side you're on?
https://www.businessinsider.com/elon-musk-tesla-spacex-secre...