Source: https://aspengrovestudios.com/quick-tip-how-to-create-a-sticky-footer-in-divi

This is to always show the footer at the bottom of the page, even when there is not enough content to fill the screen.

From your dashboard, navigate to Divi » Theme Options » Integration » add code to the body.

Here is the code:

<script>// <![CDATA[
var th = jQuery('#top-header').height(); var hh = jQuery('#main-header').height(); var fh = jQuery('#main-footer').height(); var wh = jQuery(window).height(); var ch = wh - (th + hh + fh); jQuery('#main-content').css('min-height', ch);
// ]]></script>
Code language: HTML, XML (xml)

Alternative for in the Divi code module on a specific page or in the custom css (via Jurrie Eilers):

<style>
#main-footer {
 position: absolute;
 bottom: 0px;
 width: 100%;
}
</style>
Code language: HTML, XML (xml)