If you are good at creating, you can create notebooks and other digital products. You can sell these on Amazon, but you can also sell these on Etsy. Create a digital product, then add a download button, and you have it set.
If you have some technical skills, you can use those skills to be an app. That can be an app about anything that people will find value in. For instance, you can have a finance app, a recipe app, or even a fantastic travel app.
Investing in the stock market is one of the simplest ways to create a passive income stream. You can continue to buy these index funds and allow compounding interest to really grow your money.
Creating a course is much like writing a book. There are many skills out there that people would be willing to learn if they had a good course that can teach them. If you can teach someone, then building a course is a great way to generate some good residual income.
Starting a blog can be challenging work that takes time and money to make things happen. If you want to capitalize on something with a high ROI, creating a blog can be a way you can do it.