A.ts

import type Target from "./Aa";
import type { TNode } from "./Aa";

interface Interfo { enact(target: Target): void; }

export default class Implem implements Interfo {
}

Aa.ts

export default class Target<T0 extends TNode = TNode, T1 extends TNode = TNode>
{
}

export type TNode = Target | null;

tsconfig.json

{
  "compilerOptions": {
    "strict": true
  }
}