* For example, see https://news.ycombinator.com/item?id=10905937

* Mobile-phone baseband chipsets are proprietary and secret a.f. and part of that is down to the carrier's insistence.

* Baseband chipsets run software that the carrier ships OTA to the phone.

* While baseband chipsets are ostensibly part of the wireless modem and meant to simply provide a service to the rest of the phone it looks like they generally have some form of access to the phone's main memory bus (just like any other PCIe device in a PC) and so could read the framebuffer (assuming it's backed in RAM at all) - or at least the back-buffers of the screens of running applications.

* Even 6-7 years ago, there existed definite causes for concern in (at least) the 32-bit version of iOS - but I can't find any hard evidence that the baseband chip in Apple Silicon-era phones wouldn't have at least some access. See https://github.com/userlandkernel/baseband-research

walled-off from the rest of the phone (somehow) from what I can tell it looks like

A useful search term here is IOMMU, the major phone platforms have readily available documentation describing the architecture and its security goals.

We have way, way, way more than that. Both the GP and you are arguing about the security deficiencies of modern phones as you've imagined them, rather than as they are but that gap is trivial to close with relatively little reading.

I appreciate the strength of your conviction - but I'm not an phone industry insider, and have no access to the kinds of reading-material I assume you're pointing to - for example, Qualcomm put their docs behind a verify-your-employer-wall (which is outrageous): https://www.qualcomm.com/products/technology/modems/snapdrag...

...if Qualcomm's attitude towards openness and transparency is representative of the mobile comms industry in general then they have little hope of correcting any misinformation or misconceptions other technology folk like ourselves might have, let alone the general public.

The baseband parts here are not, as message board C.W. would have it, top secret unknowable wizard hardware. You can get the part numbers and look them up.

There's a lot of weird mythology about these modem parts. The thread you linked to included someone claiming that basebands were DMA'ing into host memory --- you couldn't even do DMA over the HSIC USB the parts were using. Like, it wasn't even physically possible.

(I have no idea what a 5G Snapdragon Xwhatever can do today, but I assure you that Apple's security team does).

Given the amount of spying that has been revealed (a lot of it seeming to be superficially illegal) it seems reasonable to assume that phones are compromised in all manner of ways unless proven otherwise. I'd prefer to be pleasantly surprised.

Anything that makes it more expensive for the government to read someone's communications is a bonus. Ideally panopticon states will remain uneconomic.

A GPS transponder with microphone and camera under the control of billionaires seems like a mistake

Likewise, you can highlight text on screenshots.