"Publicly available" is different from "licensed under a FOSS license". Anyone other than the original author doesn't have the right to distribute, modify or even execute the code.
Even if the code is licensed under an open source license, in most cases it requires users to attribute the original author, while in some cases derivative work must be licensed under the same license too.
GitHub Copilot use the code without honoring these obligations.
You grant GitHub a license to display your code, same for Codeberg, they're not bound by your license because you're granting them specific rights. Secondly can you prove damages when a person uses your code but doesn't attribute you? If you can't your license isn't very useful. This is what we all need to understand.
Even if the code is licensed under an open source license, in most cases it requires users to attribute the original author, while in some cases derivative work must be licensed under the same license too.
GitHub Copilot use the code without honoring these obligations.