That still doesn’t answer the question. The second sentence in the Wikipedia article about the partition plan for Palestine is
On 29 November 1947, the UN General Assembly adopted the Plan as Resolution 181 (II).
so I’m not really sure how you got the idea that this was “just a proposal”.
The article you linked says
The United States says an independent Palestinian state should be established through direct negotiations between Israel and the Palestinian Authority and not through UN action.
which makes it even more unclear. Was Israel created through UN action or did they just steal the land and expel the Palestinians? Did they negotiate directly with the Palestinians in 1948 and arrive on the agreement to share the land according to the borders that existed before 1967?
If you (or anyone) actually have an answer, I’d be happy to hear it.