We are reviewing an old sitemap which requires a refresh, and it contains the mobile tag for each URL (the site is dynamically served). Do we have to generate and upload an additional sitemap which would not have the mobile tag for each URL?
In a sitemap, this
<mobile:mobile/> tag is required and only needed for an URL that serves content especially designed and optimized for feature phones (source). Therefore, you only need to use it in that case and you shouldn't declare the same URLs without this tag in a new sitemap.