First understand the basics of ETF. There are several types of ETF but the major types are Physical and Synthetic. The physical ETF deals in real underlying asset, that means a physical ETF actually buys the underlying asset from the market. Whereas, a synthetic ETF usually deals in futures contracts of the underlying assets without actually buying the product from the market.

So you need to understand what kind of bitcoin ETF is actually being approved! If you see a synthetic bitcoin ETF has been approved, don't expect any impact on the market because the managing company is not going to buy any physical bitcoin. They will just buy bitcoin future contracts as an underlying asset.

However, if you see that a physical ETF has been approved, you can certainly expect a good spike in price because then physical bitcoins will be bought from the market by the managing company. It will create fresh fund inflow and increase the demand in the market.

I am not very optimistic with this ETF thing because several companies have shown their interest, but only Winklevoss ETF was the physical one. Rest all were synthetic.