under 50g and it depends on the physical activity of the individual. Meaning if you're a highly tuned physical machine then you can eat far more than 50g.
Closer to 50g/day, not 20....but the lower you go the more ketones your body produces.
This is a net/gross carb confusion. Less than 50g including fiber, or 20g excluding fiber.
Ketosis is a normal supplemental metabolic state that the body enters in between meals to various degrees. There's no hard black/white macro requirement.