In my case I use the "store" module. And I have the same problem export = syntax in the lib.

To solve my problem, I created file

types.d.ts

declare module 'store' {
  export interface StoreJsAPI extends globalThis.StoreJsAPI {
     // your methods to overwrite
    method(options?: any): any;
  }

  export const store: StoreJsAPI;
}

and in my ts file

import * as store from 'store';

store.method({})

And it let me extend lib types with export = syntax :)

I hope It helps somebody :)