I built an open-source multiplayer online system; I made a game with it, together with a company that had an IP and used Unity, that sold 250.000 copies almost for free.
Now that the system was proven I tried selling it to bigger B2B clients, but failed because I didn't really want to. Instead I'm moving into making things closer to the consumer, a HTML5 client for 2D and a C+ client for 3D.
Recently I realized, if I don't have a way to charge customers the whole stack is not going anywhere so I'm now in the process of adding subscriptions through github sponsors and prepaid through itch.io.
Now my engines (2D and 3D) are nearing the point where making the games is the only remaining thing to do and getting started on that beyond solving the technical unknowns is really hard, procrastination hides in the undecided subjective details.
However I believe that the only thing you can do is to make good _finished_ products and learn. Eventually you will get a break and then you'll have to handle the other side of the coin: being successful. Which BTW is harder than most think.
The hardest part is to make the software so good that you are not ashamed of selling it. Then having the courage to actually sell it, put a price tag on the thing! The rest usually happens automatically eventually; people can sense if you want to sell things, and they will exploit that, in other words: people will buy what they can afford if they sense a good deal.
Selling works best if you are confident: the interface is proven and has little friction, but you need to figure that out manually by doing it. B2B and B2C are surprisingly similar if you remove the wrapping, it's still about "how much of your time will they take away"!
The end goal is to build something that works and makes money without taking any of your time.
TLDR: Figure out your interface so that underlying complexity can be provided simply without friction while pushing closer to the end customer!
The rest is luck.