Well, my source (quoting some "Federal Environment Agency") says it does contribute to microplastics. Some googling seems to confirm this.

It is likely a fraction of a fraction of an already small fraction. Textiles, tires and food packaging are the biggest contributors. It has yet to be proven that microplastics are directly linked to any harm, it is mostly unknown.

If you care about that kind of stuff the best thing you could do is stop driving.

It depends on what you mean by "contribute". Multiple studies put half-life of PLA microplastics at a range between weeks to a month (e.g. https://www.sciencedirect.com/science/article/abs/pii/S02697... ), so they can't create a persistent hazard.