This is the 'somewhat' U-shaped Curve. The units on the bottom are Sodium Intake (as you mention above). You need to multiply this 2.5 to convert to table salt (due to table salt also having chlorine in its chemical composition).
On the left is All-Cause Mortality. Basically it's the death rate for all people, regardless of cause of death, including cancer, auto accidents, and of course heart disease. This is probably the best measure, because if, for example, deaths due to heart failure go down 10% by cutting salt in half, but the cancer rate triples, guess what - you lose.
Of the numbers on the below chart, the lowest points are between 4.0 and 5.5 grams of Sodium per day - which is where I'd want to be on this curve. It's basically TWICE the 'recommended' amount of 2.3 grams. Also worth noting that at 2.3 grams, the curve is starting to get quite steep as you cut back further (i.e., more dying) while if you go above 5.5 grams, the increase in deaths is very gradual.
So as Dr. Berry somewhat says: eat as much salt as you like, but don't dump huge quantities on your food thinking you'll be healthier.
And my disclaimer: Don't listen to any of the above as I'm not a tool of big pharma.
(now, back to fighting the Globalists and Neocons here on Ukraine)