由于您已经完成了Auth credentials，您可以使用此简单函数在Google Drive中创建文件夹。

clientViaServiceAccount(credentials, scopes).then((http_client) async {
              var _drive = v3.DriveApi(http_client);
              var _createFolder = await _drive.files.create(
                v3.File()
                  ..name = 'FileName'
                  ..parents = ['1f4tjhpBJwF5t6FpYvufTljk8Gapbwajc'] // Optional if you want to create subfolder
                  ..mimeType = 'application/vnd.google-apps.folder',  // this defines its folder
              );
            });

我来晚了，但我希望我会为其他谁想要得到文件夹的ID的帮助，这个代码我转换为一个Flutter从Java代码从谷歌官方Google Official Workspace.
首先，你可以创建一个dart类来验证用户：

import 'package:http/http.dart' as http;

class GoogleAuthClient extends http.BaseClient {
  final Map<String, String> _headers;

  final http.Client _client = http.Client();

  GoogleAuthClient(this._headers);

  @override
  Future<http.StreamedResponse> send(http.BaseRequest request) {
    return _client.send(request..headers.addAll(_headers));
  }
}

然后创建文件夹函数：

import 'package:YOUR_APP_NAME/google_auth_client.dart';
import 'package:googleapis/drive/v3.dart' as drive;
import 'package:google_sign_in/google_sign_in.dart' as signIn;

  Future<String?> createFolder() async {
    final googleSignIn =
        signIn.GoogleSignIn.standard(scopes: [drive.DriveApi.driveScope]);
    final signIn.GoogleSignInAccount? account = await googleSignIn.signIn();
    final authheader = await account?.authHeaders;

    var client = GoogleAuthClient(authheader!);
    var driveFile = drive.DriveApi(client);

    // File's metadata.
    var fileMetadata = drive.File();
    fileMetadata.name = 'test';
    fileMetadata.mimeType = 'application/vnd.google-apps.folder';

    try {
      var file = await driveFile.files.create(fileMetadata);
      print('Folder ID: ${file.id}');
      return file.id;
    } catch (e) {
      // TODO: Handle error appropriately
      print('Unable to create folder: $e');
      rethrow;
    }
  }

这将创建文件夹，并为您提供文件夹的ID，您将使用该ID将文件上传到该文件夹。