My understanding is the French feds had no issue simply enacting a law that allowed them to remotely activate microphones and cameras. Whether that means they always had the capacity or need to hijack devices with zero days/backdoors I can't be sure but it wouldn't surprise me in the slightest if they simply had remote access handed to them on a plate.

We desperately need open source, open hardware phones with something like graphene os. Otherwise I think it's safe to assume the feds have root access to all devices.