If only I knew how to make bank easily...
It's easy to make a million dollars, if you don't mind working hard to do it.
Taking out getting really lucky (through marriage, parentage or career or investment opportunities) there's two few approaches, broadly speaking.
The best approach is to become a business person. Pick some boring business, like moving widget X from where it's cheap to where it's expensive. Or be a plumber or electrician. Provide a service, like financial advice where you can skim off the assets of your clients. With some years of diligence and attention to detail you will probably be multi by the time you are in your 40's.
Unfortunately this is unlikely to appeal to an INTP. Unless it does, don't even try! The many STJ types will cream you, if you even get off the ground. The best advice I can give a young person is to first know your type, and then don't try to beat a different type at their own game. You can't do it, other than perhaps in the short term.*
The other way is boring, isn't fast, but it
will work and is the best approach for an INTP. Start saving and investing early and do it for 20-30 years. It won't take much work on your side, other than having a career that enables you to make monthly investments, but as I said above everybody here should do this. It will force you to stay in a regular paying job (or revenue stream), and will pay off when you need it eventually.
* Small caveat, with luck you might win the really big prize by doing it better, because you're the long exception. You see these examples, like Larry David who is an INTP popular comedian (I'm convinced he's an INTP at least). He is continually trying to drop out, you should read his life story on that, but his taking things out of context humor made him very rich and popular as a writer and producer of Seinfeld.