Mobile smart actions appear as a single action element in the page layout editor. However, they appear as many actions in the action bar in the Salesforce app. The bundle of actions element is varied on each supported object, example: you will see New Opportunity in Account, but not in Contact. You can refer all actions available in Mobile Smart Actions from this document.
You can’t change which actions are included as part of a mobile smart actions bundle, example: you would like to remove New Event action from Case, the solution for this is to remove Mobile Smart Actions, then add the individual actions in the object page layout or Global Publisher layout.
If you have the individual action such as New Task in Salesforce Mobile and Lightning Experience Actions page layout for Account, then you also have Mobile Smart Actions for the same Account layout, New Task will appear twice in the Salesforce mobile app, but only one New Task in Lightning Experience.
New Task appears twice in mobile app
New Task appears only once in Lightning
Reference: Mobile Smart Actions