The user action with confirm uses the User Control Confirm Panel. Below I show you an example of how this user control is the one that has the modal functionality.
From a Web Panel you must start by generating a User Control.
Then creating an empty Web Component and also a User Action.
Now go to the Web Panel events and create the following:
To clarify, the WWPAux_WC is the name of our empty WC.
We can see in the first image all the necessary controls, firstly a WebComponent, and secondly the ConfirmPanel. We also highlight the different properties of the confirm, such as the buttons that you want to implement (it can be none), and the type of body, which can be a webcomponent or html. Finally, the added user action is only a button to call ConfirmPanel.Confirm(), but it is not necessary, the idea is that .confirm() can be executed from any event.