Which option cannot be set as the On Click Destination for a Button in a Screen?

The option that cannot be set as the On Click Destination for a Button in a Screen is Block. In OutSystems, the On Click Destination of a Button is intended to specify the action that will occur when the button is clicked. This action can involve navigating to a new screen, executing a client-side logic via a Client Action, or redirecting to an external site.

Blocks are used to encapsulate reusable components and do not serve as navigational destinations. They are typically incorporated into screens rather than acting as independent navigational targets. Therefore, it would not be appropriate to set a Block as an On Click Destination since it does not lead to an alternative view or action that a Button is designed to perform.

In contrast, setting a Button to navigate to a Screen allows users to go to another defined interface, executing a Client Action provides specific, reusable logic on the client-side, and directing to an External Site opens an entirely different web address, all of which are actions consistent with a Button's functionality.