"Advanced Flow for Agentforce Superbadge Trailhead page"

Even I can't access it. Salesforce does retire older trailhead content from time to time but I wish they did it more cleanly. For example, the help page for this superbadge and the free promo org signup page continue to exist. Anyway, if you still intend to do it just for the sake of getting some hands-on (without points or a shiny new badge to showcase on your profile...), lookup some youtube videos or blogs where they have probably posted the solution.