It can be a signal of shortage of physical gold, that I doubt of, but it can be signal that gold investors try to redeem their Gold ETF shares and convert it to either cash or other assets that look more promising in their view now, like Bitcoin.
Hi tran
It cannot be a signal that gold investors are selling ETF shares because the price chart shows that gold investors are buying

There is a shortage in gold - in silver even more. Silver is going
nickel*
Declining ETF inventories while gold investors are buying signals shortage:
ETFs are treated as a source of metal when you can't find metal on the market.
Another signal of the shortage are premiums.
Premiums are always - by definition - a sign of shortage.
Currently gold spot $1160
In Shanghai $1190

$30 premium over spot per ounce
The most important part of this is, unlike New York and London - the two major trading hubs by volume - Shanghai doesn't trade gold derivatives, the SGE (Shanghai Gold Exchange) and the SFE (Shanghai Futures Exchange) trade physical.
Shanghai is physical gold, not paper gold, so to speak.
If in Shanghai gold gets traded at 3-4% premium, there is only one reason. Shortage.
* The LME suspended nickel trading at 08:15 am on 8 March 2022, and, at 12:05 pm, cancelled all nickel trades entered that day before the suspension took effect. The total value of the cancelled trades was US$12 billion.
The LME's justification for the suspension and cancellation was that the nickel market had become "disorderly", and participants' exposure posed a systemic risk to the broader market.
Between 4 and 8 March, participants met nearly US$16 billion in margin calls, with the growing perceived risk of some of these participants defaulting and facing insolvency.
...and after this gold digression, now back to BTC spot ETF Tracking!
