First, no, "radio propagation" is not "via atmosphere". Different wavelengths get absorbed, reflected, or simply passed by different parts of the atmosphere. There is no one general rule. Many of our radio communications within the atmosphere are pretty much like they would be in free space, for example.
Second, all radio waves propagate infinitely in free space. There is no finite end to the propagation. What does matter in a practical sense is signal to noise ratio. Below some signal to noise ratio for whatever information encoding scheme is used, that information can't be recovered. Or more accurately, the error rate goes up as the signal to noise ratio goes down. At some point the errors in the information make is useless or "unreceivable" in a practical sense.
You are now asking specifically about "commercial FM", which I take to mean radio at around 100 MHz (3 meter wavelength). The primary mechanism limiting reception distance of such commercial FM stations is the curvature of the earth. The wavelength is too short for significant refraction around the earth, as happens with commercial AM at around 1 MHz (300 meters). Note that when you are in a car listening to a FM station at the fringe of its range, it will come and go as you get to tops of hills or dip between them.
Another factor is that here on earth there is significant interference from all kinds of unintentional broad-band radiators. Eventually at some distance the intended signal becomes too small relative to this background noise for the signal to be picked up well enough for your liking.
In the end, there are no hard limits and reception is about signal to noise ratio. That means you can extend the useful range of a transmission by reducing noise or selectively amplifying the signal. Note that spaceprobes usually emit only a few Watts or tens of Watts, whereas commercial FM stations usually a few kW. One important difference is that spaceprobe signals are picked up with highly directional antennas and extra low noise receivers. You wouldn't want to pay for one of those receivers in your car. The narrow beam of the receiving antenna greatly increases signal to noise ratio. Since the signal is coming from a point, the same signal is still picked up along a narrow beam. But, only a tiny fraction of the noise that is coming from all around is picked up along that same beam.