const model = {
  normalKey: 1,
  coRRupTkey: 2,
  innErKey: { 
    x: 3, 
    Y: 4 
  },
  aRR: [
    { first: 5 }
  ]
}

function getModel(model) {
  return new Proxy(model, {
    get(obj, prop) {
      if (prop in obj) return obj[prop]
      const lowerProp = prop.toLowerCase()
      const ownProp = Object.keys(model).find(k => k.toLowerCase() === lowerProp)
      const value = obj[ownProp]
      return value instanceof Object ? getModel(value) : value
    }
  })
}

const wrapped = getModel(model)

console.log(wrapped.corruptKey)
console.log(wrapped.innerKey.x)
console.log(wrapped.innerKey.y)
console.log(wrapped.arr.map(x => x.FIRSt))