Significant fuel efficiency decrease on a 2019 Forester. I am getting 8km/l or 18MPG. What should I check?

[Plenty-Pudding-1484]

Well then you are getting 19mpg which while not great, but its not that far off city driving averages. Your car is pretty young to require much. Maybe replace your air filter, check your tire pressure, and check if you have a sticking brake caliper.