According to the knowledge sources provided, the maximum attribution window in Mixpanel is 366 days. This information can be found in the Funnels documentation, which states:
"The maximum amount of time you can choose for the conversion window is 366 days, or otherwise equivalent (12 months, 52 weeks, etc)."
It's worth noting that this maximum applies to both Funnels and Flows reports in Mixpanel. The same 366-day maximum is mentioned in the Flows documentation as well.
