Seems most likely this one: "Gut dysbiosis leads to cognitive decline through CNTF-mediated activation of microglia in mice" https://link.springer.com/article/10.1186/s12915-025-02454-x

The underlying mechanism seems applicable to humans too, but it's annoyingly ironic that the paper mentions mice in the title clearly and doesn't even mention humans, and the article doesn't mention mice even once.