Does cryptocurrency ETF use block-chain technology? As you know, one of these days trends is cryptocurrency ETFs that the CES doesn't approve it yet. But there are some questions about them and their functioning. Is it necessary to build them over block-chain technology? If yes, would someone explain it? and in case the answer is no, why?
Question: In other words, the main question is about how do they implemented and function.
Is it necessary to build [Exchange Traded Funds] over block-chain technology?

No.

in case the answer is no, why?

Imagine an ETF based on stocks in gold mining companies. Those companies own open-cast mines and rock-crushing machines.
An exchange can buy and sell shares, or funds based on those shares without directly themselves operating any open-cast mines or rock-crushers.
Rock-crushing machines are not suited to keeping track of sales and purchases of stocks and shares, or of funds based on them.