Publish open source game on GitHub

If it's your code, then it's your code. You can do whatever you want with it.

You can run into issues if your game includes something like a paid asset from the assetstore, or some other sensitive library that you do not have distribution rights to.

When people post their game's code, they sometimes just post the core logic and proprietary work as a resource to others. This way their creative works are disbursed and available to the community without damaging the property rights / monetization of another developer.