Some functionality of Sitecore Forms, like client validation, conditions, and so on, might work incorrectly due to missing scripts that must be loaded before a form is rendered. The following JS error might appear:
Uncaught ReferenceError: jQuery is not defined
Out-of-the-box, Sitecore Forms require an additional MvcOuterLayout.cshtml file to load scripts defined in a form item, in the Scripts field. To add it, a user should follow the "Add the MVC layout" section in the official Sitecore documentation. Note that the scripts referred to are loaded by the @Html.RenderFormScripts() helper and they are physically stored in the your_root/sitecore modules/Web/ExperienceForms/scripts folder.
If a user needs an alternative solution, it is possible to add scripts generated by the @Html.RenderFormScripts() helper manually by themselves, as shown in the following files:
ScriptsSC9.0.0-9.0.2.txt
ScriptsSC9.1.0-9.2.0.txt
ScriptsSC9.3.0-10.1.txt