Object.hasOwn property is possibly undefined TS

tsconfig.json:
{
“compilerOptions”: {
“strict”: true,
“lib”: [“ES2022”],
“exactOptionalPropertyTypes”: true
}
}

interface Shape {
  kind: "circle" | "square",
  radius?: number,
  sideLength?: number
}

function getArea(shape: Shape): number | undefined {
  if (shape.kind === "circle" && Object.hasOwn(shape, "radius")) {
    // 'shape.radius' is possibly 'undefined'. ts(18048)
    return Math.PI * shape.radius**2;
  }
  else if (shape.kind === "square" && "sideLength" in shape) {
    return shape.sideLength**2;
  }
  return undefined;
}

const s1: Shape = {kind: 'circle', radius: undefined};  // if i try this
/* Type '{ kind: "circle"; radius: undefined; }' is not assignable to type 'Shape' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
   Types of property 'radius' are incompatible.
   Type 'undefined' is not assignable to type 'number'.ts(2375) */

why this undefined error? What is missing?