@Alpha-Team after some investigation, it looks to me that the Opera forums don't use the widget system for their footer. Instead they use a hard-coded customization to the footer.tpl
template in their theme.
If you wish to do the same, you can make a similar change with nodebb-plugin-customize.
footer.tpl
........
<div component="toaster/tray" class="alert-window">
<div id="reconnect-alert" class="alert alert-dismissable alert-warning clearfix hide" component="toaster/toast">
<button type="button" class="close" data-dismiss="alert" aria-hidden="true">×</button>
<p>[[global:reconnecting-message, {config.siteTitle}]]</p>
</div>
</div>
<!-- ENDIF !isSpider -->
<footer>
==== Your footer goes here ====
</footer>
<script defer src="{relative_path}/assets/nodebb.min.js?{config.cache-buster}"></script>
{{{each scripts}}}
<script defer type="text/javascript" src="{scripts.src}"></script>
{{{end}}}
........