No, because brain signals are so low voltage compared to silicon voltage thresholds that if you put a diode in to block outgoing signal, it would just reduce all incoming signal to noise. On an IC where there is very fine silicon property control it is probably possible though.

Let's say that it is possible, it would still have to be implemented on the PCB or more likely, the IC itself. Guess who's literal job it is to design and make all of the decisions on what is possible would be? The exact same people who would benefit financially from enabling that functionality and serving ads. The point of all of this is that there are 1000 ways to make that functionality not be available on the design, but the decision to make it available or not is made by the people who would earn a lot of money from it and benefit directly.

Every single major technology that has the ability to display ads eventually does, without fail. Every single one. Why would an implanted chip made by the same companies be any different?

Again, I think it will be a VERY long time before we have the sort of fine control and deep understanding of the brain to effectively control sight and sound. I think 20 years might have actually be generous and it might be 30-40 unless we hit a breakthrough in biological computing or something.

Until then, there would be absolutely nothing to worry about. Musty's "brain chip" would never have this capability and would be much more likely in causing strokes than any other danger.

The problem is that if it is unquestioned, implemented, and normalized that "everyone has a brain chip" then, just like smart phones, they will slowly change until the tech does become available and maybe they just have an ad on startup, maybe they just have an ad here or there, until the entire thing just becomes a vehicle for ads like smartphones are now.