Our recommendation to acomplish this would be to build a widget for the landing page (https://docs.q2developer.com/guides/frontend_development/widgets.html) and use its execution to launch a modal (https://cdn1.onlineaccess1.com/cdn/base/tecton/v1.9.8/Documentation/index.html#/capabilities/showModal) or overpanel with the tecton javascript.
There would be no UI to the widget itself, just Javascript to launch the modal or overpanel.
Thanks Ryan for the information.
We are potentially working with a various FIs that have asked for a similar modal interrupt prompt after login. We will share your suggestion with them, but if they still really want a modal interrupt page after login, is there a way to do it?