50g is the absolute highest threshold I’ve ever seen recommended. Far more common are 30g (low enough for most) and 20g (low enough for basically all). 50g, while low enough for many, is far too high to induce ketosis in a lot of people and thus is a poor recommendation.
Edit: one note about your linked keto guide by the way: it references high protein intakes suppressing ketosis due to amino acids having the potential to convert to glucose. While this conversion is real, there’s a decent body of evidence to suggest this process of gluconeogenesis is demand-driven, not supply-driven, so even fairly high protein intakes of ~200+g per day are unlikely to have much of an impact.