Indeed, no matter how it is defined, scientists agree that multicellularity has occurred multiple times across many clades. Defined in the loosest sense, as an aggregation of cells, multicellularity has evolved in at least 25 lineages. However, even when defined more strictly -- requiring that cells be connected, communicate, and cooperate in some fashion or another -- it has still notably evolved once in animals, three times in fungi, six times in algae, and multiple times in bacteria.
https://www.sciencedaily.com/releases/2014/01/140125172414.htm
Multiple times independently!