The 'Modified on' time stamp displayed when viewing the solution article can be hidden with the help of the Complete layout customization feature which is available from the Estate plan.
Please follow the below steps to remove the article modification timestamp when viewing a solution article.
1) Please go to Admin>Channels> Portals>Customize portal>Layout & pages>Portal pages>Article View.
2) Exclude the below code snippet -
{% translate portal.article.modified_on %} {{ article.modified_on | short_day_with_time }}