For my understanding of the ETFs, people are just trading air during the session. After checking on the balance of buys and sells after market closes the emissor of the ETF needs to go to the real market and buy or sell the Bitcoin.
If that's true, what happens if Bitcoin starts to go parabolic? Today Blackrock (for mention a random ETF emissor)would have to go and buy thousands of Bitcoins at 65K, 70K or more. How convenient that the crash of the app stopped the run and now they can buy all that Bitcoin at only 60K.
Just saying