The Joomla Editor API allows for a number of additional buttons - editors-xtd buttons - including Joomla core buttons like Article, Image Read More, Pagebreak, Fields and Modules, as well as buttons from installed extensions, that are usually displayed below the editor.

Editor-xtd buttons rendered below the editor
Editors-xtd buttons displayed below the editor

In some extensions which do not use the Joomla API to render the editor, such as SP Page Builder, these buttons cannot be displayed in their original form. JCE includes a special button - the Joomla button - to collect these buttons into a list menu, accessed by clicking on the button in the editor toolbar. You can then select and click the editors-xtd button option you require, as you would if clicking the button below the editor.

Joomla Menu Button
The Joomla menu button showing the editors-xtd buttons as menu options.

You can add this button - identifed by the Joomla logo as its icon - to the editor toolbar in the Features & Layout tab when editing an editor profile.