According to Scott Manley’s video on the topic the probes would need to arrive at the correct time in order to form what is effectively a huge phased array antenna.
Only then is the combined transmission power of these tiny probes large enough to be received on earth.
NASA Selects a Wild Plan to "Swarm" Proxima Centauri With Thousands of Tiny Probes (www.sciencealert.com) angielski