There will be some cliche ways here that most people will tell you. but I will try to compile some lesser-known.
1. Making Games
I think making games is the most fun on this list.
Well, you can make games even if you have no previous knowledge. You can learn a game engine like Godot, Unity, or Unreal Engine
Have experience in Python? use Pygame, know Javascript use Vanilla Javascript or any game framework there are many for Javascript, know C# better for you, you can directly learn Unity a Unity uses C# as its main scripting language, Java? learn Libgdx or LWJGL which is Minecraft based upon
Why should you make games?
Well, you will learn a lot especially if you chose a Framework or Library rather than some game engine and it is some different fun to write our own thing than making the game engine do everything for us Secondly, it is a great way to make quick money many indie developers have made money in just a few months. I am not saying to create the next Minecraft or Terraria I am saying to make mini-games that would be fun to play and also make gamers happy. It can be any game but just fun to play so that gamers could buy.
You can sell games on platforms like itch.io or games can be free and players can donate.
2. Freelancing
If you spent any time researching about earning through code Freelancing is what most people would recommend as it is from where you can get the most experience in business from
In my experience, the most important thing to avoid is freelancing sites like Fiverr and Upwork and find your clients on your own and social media as these platforms are very saturated and it becomes a lot difficult to find new clients.
What is Freelancing?
Freelancing is nothing but finding paying clients to do work. It doesn’t matter where you find your clients or from where they contact you.
It doesn’t matter what skill you have you can get clients even on jobs like data entry in Excel
3. Create Udemy Courses
This I think is the most profitable
If you have a good understanding of anything from creation to coding you can teach on Udemy or any other service that will take your videos for free.
on Udemy you can just scroll to the bottom and click become a teacher you can upload videos create a course and students will pay for your course and that’s how straightforward it is.
4. Start a YouTube Channel
It is just one of the cliche ones but it can profit you if did right. I know YouTubers like Andres Vidoza who grew their channel way more than a thousand subscribers in less than a year which is of course when you can start yearning through youtube ads
But even before that, you can yearn through affiliate links, selling your own products, and much more.
5. Start Your own Business
This will give you the most Profit and Experience if done right. If you are a developer you may think of creating your own app own software to solve or automate day to day lives of common people. Building a business around something that will benefit your future as well as your customers.
Finding an idea to build a business around is not difficult most of the companies are started to ease something that people are struggling from
Apple was started as Steve Jobs wanted to have computers in every home. PayPal was formed to ease international transactions. Amazon was created to ease buying and selling local and international products.
In the same way, you can also find something you or your known are struggling with. The same problem will be in others' lives too. Help them and they will be your customers.