Toyota at least has an opt-out website. (Or at least in the US they do). You lose the ability to do stuff like remote start from your phone though. And emergency roadside service, blah blah blah. I turned off all the mapping saved route stuff immediately that let you see your previous trip average miles/KW and then turned off everything once they wanted me to pay a monthly fee for remote start and such.

No shit , this just in said anyone in security.

Is there any open source/privacy focused connected car software?

I'm shocked, i tell you, shocked!

I mean if you're mechanically talented enough and sufficiently motivated, you could probably rip out the digital controls and replace them with mechanical analogs, getting rid of the computer entirely. Extremely difficult, but probably doable if you know what you're doing.

That aside, we shouldn't have to do that to get out of being spied on.