Basic explanation:
The note in a trigger "Not executable" refers to manual execution. This means that you cannot drag the slider to the side in this case and thus move/switch the devices to the specified state. However, the trigger works with the selected event.
The note in the slider is a bit misleading. It should actually say "Cannot be executed manually" (due to space limitations, this has not been implemented yet).
Background:
With the update 5.7.x we have the possibility to add devices and groups directly to a trigger. You don't necessarily need a scene anymore. The slider to execute was not available in the triggers at all until now.
Example:
A trigger with the event Time, which then moves 2 shutters to a target position, displays: "Not executable". However, the automatic is implemented.
When is a trigger manually executable?
You have to create a trigger and select "Manual execution" as event. In this case, you can use the slider to control the devices, groups or scenes according to the targets.
How can I execute an existing trigger manually?
Call the existing trigger and duplicate it. Then change the event to "Manual execution".