Is this actually feasible for some decent percentage of cars nowadays? If so, where did you research?

YouTube. I think in most cars it’s gonna be a discrete component that can just be unplugged. The big question is what functionality you lose, and whether you can live with that tradeoff.

Anecdotally, my 2023 Kia's infotainment unit is one big plastic box that I was able to access by just prying up some plastic and undoing a handful of screws.

I was applying some dielectric grease to the USB port used for Android Auto (in order to prevent intermittent disconnects while driving) but I wouldn't be surprised if one of the many other cables plugged into it led to a cell antenna on the exterior.

There are also software options; I was able to disable the "telematics" in the same vehicle by inputting a (frankly schizophrenic) combo of rolling back the date, touching random invisible trigger zones in menus, and entering a leaked PIN to access the appropriate service menu on the infotainment unit.

Figuring all that out was unfortunately quite difficult, although I imagine you might be able to get "official" help if your local dealership is friendly and willing to bend the rules. I had to settle for a lot of keyword massaging on Google.

> I was able to disable the "telematics" in the same vehicle

This is only sufficient if you trust software, which you shouldn’t. Hardware disconnects are reliable. Cut the power.