foreach (var document in documents)
{
    using var stream = (RecyclableMemoryStream)RecyclableMemoryStreamManager.GetStream();

    if (utf8JsonWriter == null)
        utf8JsonWriter = new Utf8JsonWriter((MemoryStream)stream);
    else
        utf8JsonWriter.Reset((MemoryStream)stream);

    jsonDocument.WriteTo(utf8JsonWriter);
    utf8JsonWriter.Flush();

    var memory = stream.GetReadOnlySequence();

    using var cmd = new NpgsqlCommand("INSERT INTO mydocuments (id, document) VALUES (@document)", conn);
    cmd.Parameters.Add(new NpgsqlParameter("document", NpgsqlDbType.Jsonb)
    {
        Value = jsonDocument,
        ConvertedValue = memory
    });

    cmd.ExecuteNonQuery();
}