The development of multicellular life is unlikely to be the great filter. According to Wikipedia, "Multicellularity has evolved independently at least 25 times

The development of multicellular life is unlikely to be the great filter. According to Wikipedia, "Multicellularity has evolved independently at least 25 times in eukaryotes". https://en.wikipedia.org/wiki/Multicellular_organism#Occurrence https://en.wikipedia.org/wiki/Multicellular_organism#Occurre... Evolution of eukaryotes from prokaryotes is a more plausible bottleneck. (Disclaimer: I am not an expert on any of this.)