There have been some experiments on megadosing probiotics to help with social anxiety disorder (SAD). There is at least this one guy who says it fixed it completely. He makes a megadose by growing specific probiotics in milk.[0]

This is different however, because the article talks about early brain development and autism spectrum disorder (ASD). Maybe early microbiome disruption -> ASD, later -> SAD?

[0] https://pdfcoffee.com/experimental-treatment-for-social-phob...