Bitcoin ETF or the actual thing?

I have been investing in S&P500 and Nasdaq for a few years now. And I'm going for long term, to have a better future for my family. Just recently I got into Bitcoin (yes, I bought at 120k). Bitcoin ETF, that is. Because it seemed like a good way to start out. Since then, I read a lot about it, and I kind of believe in it, or at least see the potential and the future.

But I'm getting into a paradox right now. Because if I believe in it, should I be buying Bitcoin ETF on an old-fashioned stock market which Bitcoin is going to take over?
But at the same time, I'm a chicken and have a busy life, and don't really like the idea of cold wallets and handling all myself. I really like the idea of DCA'ing the hell out of it for the next 20 years via my broker that has all my other investments.

But in, say, 20 years, when I actually want to sell and enjoy life, or buy a house for my son, is there anything left to sell, because Bitcoin has taken over? How much worth is my ETF then if the whole financial system changed? And if so, will only the ones with the real Bitcoin profit, or will the ETFs just keep rising with it?
Can I have it both ways, or will I have to chose at one point (and is that point now)?

What I think I'm saying is that I believe in crypto and BTC, just like in the S&P500, so I am willing to invest in it. But to actually start implementing the whole idea behind it...

This all kind of dazzles me, as a (relative) newbie to stock markets, let alone Bitcoin.