You have to do you own thing. Find something where you are good at. It doesn't work replicating someone else success because circumstances are different. And you might not have the same type of skills that are required. What worked 5 years ago is not relevant anymore. Especially on the internet things keep evolving fast.
That's why passive income and the internet are mostly bullshit. Nothing is really sustainable or passive. Even renting out properties is not because you have to maintain them and find new people who want to rent, do al the paperwork etc.
But sustainability of a business would mostly go hand in hand with it's competitive advantage. Why do people have to buy something from you and not from the competition?
Why are some corporations so successful?
Facebook, Ebay have a network effect.
Pfizer has patents to protect it's inventions from being ripped off by competitors.
Coca-cola has a very valuable brand name.
Some Chinese corporations have a production advantage because they can produce cheaper than Western countries.
Luxury brands like Gucci, Supreme, Versace they have very good marketing and can hype up the brand. In essence you just pay a premium in price for their brand name, to look cool. So they play on human psychology and use it to make a profit.
Amazon has a scale and distribution advantage over competitors.
You know what i mean? But it wouldn't work out starting your own Amazon, the sweet spot to enter that niche has already passed. You can't compete with them just like that.
It would be smarter to get into some new trends like AI or blockchain. There are still a lot of opportunities but you need to skills for it.