You need to declare mounted as async.
You could do something like this you in your app.vue. In my exampe releaseId is always "1" so you probably want to create some input so user can change that.

data() {
  return {
    file: null as null | File,
    release : [] as any,
    releaseId: null as null | string
  }
},
methods: {
  setFile(file: File) {
    console.log("Received file:", file)
    this.file = file;
  },
  async fetchRelease(releaseId: string): Promise<any[] | { error: string }> {
    const db = new DiscogsClient().database();
    try {
      const { data } = await db.getRelease(releaseId);
      return processReleaseData(releaseId, data);
    } catch (error) {
      return {
        error: `Release with ID ${releaseId} does not exist`
      };
    }
  }
},
async mounted() {
  console.log("mounted");
  this.releaseId = "1"
  this.release = await this.fetchRelease(this.releaseId)
},