VueJs3 - Reactive key in json-object

Question

Using VueJs3, composition api, I would like to have a reactive JSON object with a key that change based on user-input.

const nodes= reactive({
  nodes: {
     <reactive-key>: {
      x: 0,
      y: 0
    }
  },
})

All my attempts have failed. Does anyone have suggestions on how this can be solved?