btc hardness vs gold hardness

hello, i’m finally reading 21 lessons and there is, of course, a chapter on soundness of money. we know ultimate supply of bitcoin has ac hard cap at approx. 21 million, due to the halving and such, resulting in a ultimately high stock-to-flow which makes bitcoin „sound money“.

while i understand why that’s a good thing, the book compares this to stf of gold, indicating that btc will surpass gold in 2020 -> however - that is also true for gold as well, isn’t it? Eventually, no more gold is to be found (unless we give the alchemists stone…), so technically stf will also approach a very high number for gold, just slower?

i’m not advocating gold here, just try to find the error in my understanding :)