This Site Workflow will send a notification after querying a list, grouping notification for each recipient instead of sending one for each items.
This site workflow queries a Task Lists and notifies each assignee of a task with a single email with the list of all his tasks.
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Nintex Workflow 2010, Nintex Workflow 2013, Nintex Workflow 2016 Nintex for O365
SharePoint 2010 SharePoint 2013 SharePoint 2016 SharePoint Online
Send grouped notification based on list items to get more information about the logics