“Manually run via checkbox” is one of the steps available in the “Action Workflows” feature of the PublishPress Future Pro plugin.
This trigger allows user to manually start the workflow. This workflow trigger can be used via the post editing screen or the Quick Edit panel. You can add a “Manually run via checkbox” step from the “Triggers” tab of the “Action Workflows” area.

When this trigger is enabled, users will be able to manually enable the workflow inside posts, using this metabox:

This setting will also be available via the “Quick Edit” area of each post:

