General Assembly resolutions are helpful signposts of international law but not a binding source of international law. For something to be a point of customary international law, it needs to have jus cogens and state practice. In simple terms, countries need to believe that it is law and act accordingly.

GA resolutions are useful as statements of jus cogens (belief that law exists) but not necessarily determinative.

None of this is relevant to your question though, since the US does not abide by international law.

When you hear about “international law” it’s essentially just UN resolutions and treaties