So I am trying export my game to html5, I have the free version from steam, it is a 2d plat former, it works on localhost:50000 thing but when I export to html5 and run the index.html, it just shows a black screen. What is going on?
You need to upload your game to a web server for it to work.
Develop games in your browser. Powerful, performant & highly capable.
So I can not just export to html5 and run index.html?
This is due to browser security limitations. You cannot run the exported html 5 project locally.
Just get yourself some free space from places like Dropbox and host the project on it. Then you can share it with a public link.