Flash a message up.
If Long is selected, the message will flash up for longer.
A Flash is less intrusive than a popup: it is still possible to interact with the application below while the message is showing.
On some devices, disabling Notifications for Tasker in Android settings will also prevent flash messages.
Note: Android 12+ seems to limit too many toasts in a row.
Please check each field's help (?) button to see how to configure each field correctly.