I needed to do something similar to the promise.all just with observables and came up with forkJoin, here's an example

forkJoin.ts

  geSomethingById(id: number): Observable<any[]> {
    return this.http.get<any[]>(
      `api/something?id=${id}`);
  }


  getSomething(ids) {
    const ids = this.getListOfVersionIds(selectedArtifacts)
    const requests = ids.reduce((acc, id) => {
      acc.push(this.geSomethingById(id));
      return acc;
    }, []);
    return forkJoin(requests)
      .subscribe((files) => {
      return files;
      });
  }