@nprofile1q... Are you familiar with TR-069? It's the protocol that gives ISPs backdoor access to your routing/modem hardware. The government(s) apparently using it, though how often I do not know, and we have evidence of that now. It's another concern that I've had for ? decades ?. None of it is secret. The reps at telcos openly tell people they're remotely connecting to the routers. I don't think people fully understand the danger and what ISPs and governments in turn can do with the technology or why it's appropriate to frame it as a backdoor.

I'm not sure what you know about the modem firmware, but there exists similar problems with phones.

Most phones are built around a SoC rather than having a separate modem component. The memory between the modem and the rest of the phone is shared and accessible by the modem firmware. The cellular providers are able to update this component and while it's rare to read about it at a technical level there have been a story or two over the decades of governments taking advantage of this to get around end-to-end encryption and similar or otherwise remotely tap into the microphone and use it as a listening device. The mic is often connected directly to the modem component as well.

There are two devices on the market that I'm aware of where this isn't the case. The one I'll leave unnamed as the guy behind the company behind it is a scammer/fraudster more or less. The other is the Pine Phone. The Pine Phone uses a EG25-G chip for the modem which has it's own dedicated ram and flash. The other part of the device is using a Rockchip SoC. There are dip switches such you can disable the modem/wifi if you want. It's neat because it's possible to use external USB 4G and USB wifi adapters:

https://www.thinkpenguin.com/gnu-linux/usb-4g-lte-advanced-modem-gnu-linux-tpe-usb4g2us