There are different ways of earning passive income legitimately, the question is actually can you be patient enough? you can go start a bog, a youtube channel, write a book, get into real estate or do affiliate marketing, these are all great ways of earning a passive income, it will take a couple of years before you'll begin to see any meaningful progress, most people like the idea of earning money passively but it is not a priority for them, sort of how most people like sport cars to the extent of using them as wallpapers but most will never prioritize working on actually getting to drive and own them.
If you plan on building a passive income, first of all, you have to prioritize it, make it your number one goal, sleep with it, wake with it, think about it and most importantly take action to make it a reality, without that, it will forever remain a fancy idea in your head.