Does MsGraph v5.61.0 and SharePoint have a bug?

Hello.
It allows searching for folders in the "root" of a library using "tolower(Name) eq" but it does not allow the same in subfolders. I attach the method where I detected the problem.

public async Task<string?> FolderExistsAsync(string listDriveId, string? folderParentDriveId, string subfolderName)
{
    try
    {
        if (folderParentDriveId == null) // root
        {
            // Ok (best solution, search in server-SharePoint)
            DriveItemCollectionResponse? folderSearch = await _graphClient.Drives[listDriveId]
                                                                    .Items
                                                                    .GetAsync(q => q.QueryParameters.Filter = $"tolower(Name) eq '{subfolderName.ToLower()}'");
            return folderSearch?.Value?[0]?.Id;
        }
        else
        {
            // Ok (bad solution, search in client)
            DriveItemCollectionResponse? childrens = await _graphClient.Drives[listDriveId].Items[folderParentDriveId].Children.GetAsync();
            DriveItem? subfolder = childrens?.Value?
                                    .FirstOrDefault(item => item.Name?.Equals(subfolderName, StringComparison.OrdinalIgnoreCase) == true && item.Folder != null);
            return subfolder?.Id;

            //// Err: in Ms Graph v5.61.0?.
            ////var debugAux = await _graphClient.Drives[listDriveId].Items[folderParentDriveId].Children.GetAsync(); // Ok
            //DriveItemCollectionResponse? childrens = await _graphClient.Drives[listDriveId].Items[folderParentDriveId].Children
            //                                        .GetAsync(q => q.QueryParameters.Filter = $"tolower(Name) eq '{subfolderName.ToLower()}'");
// Err: Microsoft.Graph.Models.ODataErrors.ODataError: 'Item not found'
            //return childrens?.Value?.FirstOrDefault()?.Id;
        }
    }
    catch { }

    return null;
}

Thanks.