The Bitcoin market will be susceptible to manipulation even after all ETF applications are approved as long as there are big players like Binance in the market. If I'm not mistaken they are now the third or fourth largest holder of Bitcoin. In addition they cooperate with Wintermute which in my opinion is the main manipulator in the cryptocurrency market.
The Bitcoin ETF market will not be able to reduce volatility as high volatility remains in the native Bitcoin market.
The price of any product always stabilizes as the user base expands and adoption becomes widespread. The ease of launching ETFs will help further embrace the concept of Bitcoin as a store of wealth. Since most investors are not familiar with Bitcoin due to their lack of expertise and familiarity with the banking mentality, they will prefer to treat this investment as if it were the stock market. As the number of investors increases, more Bitcoin will be accumulated by these companies and owned by their investors, and the price will move toward greater stability, gradually moving away from its volatile nature.
When we recently saw fear in the markets caused by the introduction of tariffs on many countries, investors sold Bitcoin ETFs no less than native Bitcoin. Institutional investors and large companies are just as prone to panic as ordinary cryptocurrency investors when the global geopolitical situation is uncertain or a crisis is looming. So I don't think Bitcoin's volatility will decrease significantly anytime soon. For that to happen, countries would need to start competing to create strategic reserves in Bitcoin.