“Legally binding” makes sense within a system where a mechanism of enforcement exists. Once you rise above the state, nothing exists, at least on a permanent basis.

Ukraine is basically in a situation of “you don’t own what you cant defend through violence”.

The Ukraine will lose another chunk of territory. Western nations will “decry this violation of sovereignty” and the UN will condemn it, but Russia will own it.

People don’t like it, but in the end the US motto of “might makes right” is correct. If you cant defend it, it’s not yours.