Typescript array subset based on object keys not allowed [duplicate]

I have object properties being looped through generically, some of the number props needed additional calculations, and I ended up with this (simplified) situation. Any help would be greatly appreciated: I get an "unassignable" compile error on both lines in the main function.

interface Data {
  a: number,
  b: number,
  c: number
}
const data = {
  "a": 1,
  "b": 2,
  "c": 3
}

const ar: (keyof Data)[] = ["a", "b", "c"]

type Allowed = Omit<Data, "c">
var allowedAr: (keyof Allowed)[] = [ "a", "b" ]


function main(key: keyof Data) {
  if (allowedAr.includes(key))
    allowedFn(key)
}

function allowedFn(key: keyof Allowed) {}