When switching to the User or Custom Menus environment before creating the first form for a table, 4th Dimension asks if you want to create default input and output forms.

With the Automatic Form Creation option in the Preferences, you can for example, set 4th Dimension to automatically create default forms and therefore not display the Create Detail Form dialog box. From Design mode, open Preferences. Select the Options sub-topic from the Application topic. Change the Automatic Form Creation setting to "Always Yes for All".

You can set the Automatic Form Creation option to "Never" if you prefer custom forms.