One of my favorite examples of correlation being mistaken for causation is the correlation found between autism and low microbiome diversity in several studies. Many microbiologists assumed the microbiome differences were contributing to autism in a causal way. However, it was later shown that differences in dietary preference by neurotype were driving the differences in the microbiome. https://www.cell.com/cell/fulltext/S0092-8674(21)01231-9?rss=yes