NEW YORK/WASHINGTON, Dec 22 (Reuters) - Popular short-video app TikTok is offering to operate more of its business at arm's length and subject it to outside scrutiny as it tries to convince the U.S. government to allow it to remain under the ownership of Chinese technology company ByteDance, according to people familiar with the matter. TikTok has been seeking to assure U.S. government departments and agencies for the last three years that the personal data of U.S. citizens cannot be accessed and its content cannot be manipulated by China's Communist Party or any other entity under the influence of that...