.where将创建一个新的修改列表，但不修改原始列表。重新分配原始列表或返回修改后的列表。在这种情况下，我认为2更好，因为我们只对列表执行一次过滤操作。
同样，.where将返回Iterable，它是List的超类。由于您的函数返回List，因此我们必须使用.toList()将Iterable转换为List。
1.重新分配原始列表

final response = await httpServices.getRequest('mobileAppGetIcbsid?icbsid=001-0000055');
final jsonData = json.decode(response.data);
var map = Map<String, dynamic>.from(jsonData);
var userData = UserModel.fromJson(map);

// Reassign the result of .where to modifiedUserData
var modifiedUserData = userData.loan?.where((element) => element.status == "Closed");

return modifiedUserList.toList();

1.返回修改后的列表

final response = await httpServices.getRequest('mobileAppGetIcbsid?icbsid=001-0000055');
final jsonData = json.decode(response.data);
var map = Map<String, dynamic>.from(jsonData);
var userData = UserModel.fromJson(map);

// Return the result of .where directly
return userData.loan?.where((element) => element.status == "Closed").toList();

• 希望对你有帮助

void test() {
  var json =
      '{"loan":[{"id":"1", "icbsid": "55","loanId": "null", "status": "Closed"},{"id":"2", "icbsid": "55","loanId": "null", "status": "None"},{"id":"3", "icbsid": "25","loanId": "sss", "status": "None"} ]}';
  final jsonData = jsonDecode(json);
  var map = Map<String, dynamic>.from(jsonData);
  var data = UserModel.fromJson(map);
  data.loan?.removeWhere((model) => model.status != 'Closed');
  data.loan?.forEach((model) {
    pr('id::${model.id}  status::${model.status}');
  });
}

class UserModel {
  List<Loan>? loan;
  UserModel(this.loan);
  factory UserModel.fromJson(Map<String, dynamic> json) => UserModel(
      (json['loan'] as List<dynamic>?)?.map((e) => Loan.fromJson(e)).toList());
}

class Loan {
  String? id;
  String? status;
  Loan(this.id, this.status);
  factory Loan.fromJson(Map<String, dynamic> json) =>
      Loan(json['id'], json['status']);
}