An increase in the amount of gold bullion held by GLD (the SPDR Gold Shares) and other bullion ETFs does not cause the gold price to rise. The cause-effect works the other way around and in any case the amount of gold that moves in/out of the ETFs is always trivial compared to the metal’s total trading volume. However, it is reasonable to view the change in GLD’s gold inventory as a sentiment indicator.

https://tsi-blog.com/2019/05/what-is-glds-gold-inventory-telling-us/