it's not that either. it's the total value of all transactions.

if you paint a masterpiece worth millions and keep it in your closet it has negligible impact on GDP. only once it is sold does it have an effect.

And on the contrary, there’s this method of increasing GDP.

https://news.ycombinator.com/item?id=37395566

And if its sold 5 times in the year its 5x the GDP. Of course the value of the painting hasn't changed and their remains only 1.