Buy Bitcoin and then continue with DCA ( Dollar-cost averaging bitcoin) and after a period of time you will have a good amount of satoshis in your wallet. There price of those satoshis will grow organically and you will earn a good passive income. Don't rely on anything else in the crypto market other than Bitcoin.
Good idea, and I am a supporter of it, but it is not what is normally understood by passive income, although it is. Normally it is something that gives you extra units from what you already have, like if you have 1 Bitcoin and you deposit it in a place and it gives you 4% APR, so at the end of the year you will have 1.04 Bitcoins.
But if you buy a bitcoin today at $66K and sell half of it when the price reaches $132K, you will have obtained $66K of passive income and you will still have the initial $66K of Bitcoin purchasing power left. And all in all you will have only made a few clicks to get it.