I would guess that the rumor is partially true, but interpreted incorrectly.
I see a big hurdle in the fact that CarPlay generally relies on MFi, and if they switch from authenticated cables to non, you would lose CarPlay if you bought a new phone with an older car. So my guess is that they have USB-C cables with MFi that allow for backwards compatibility with existing systems. CarPlay would not be the only one, but it is probably by far the most prominent.
Framing is everything here.
You can say, "Apple is making special USB-C cables with MFi to ensure compatibility with existing 3rd party MFi systems"
OR you can say, "Apple is artificially limiting certain functionality over USB-C cables"
Both are "correct", but the second one is missing the point. The first is correctly including the context that prior systems will expect MFi authentication, and are not designed to work without it, while the second excludes that important context.
It could be that apple is intentionally excluding an embedded MFi authentication in its USB-C implementation, but there could be engineering reasons why doing so might compromise non-MFI connections.
I used to have access to many of the MFi docs, and always hoped to see something about MFi over USB-C, but never did.
Imagine, the EU forces apples hand and from 2023 on, you simply can't buy a new iPhone without buying a new car if you want CarPlay because for most new cars, aftermarket head units are no longer a reasonable option.