Seems this is a common issue, with no published solution, so...
I'm updating a client site to Joomla! 4, and all is not well.
The site works fine under Joomla! 3. Upgrading to Joomla! 4 causes the Full Width header to not be shown. Then if I try to create a NEW full width header under it, I'm given the following error:
() JROOT/templates/shaper_fixter/sppagebuilder/addons/slideshow_full/site.php:39
2 SppagebuilderAddonSlideshow_full->render() JROOT/components/com_sppagebuilder/parser/addon-parser.php:802
3 AddonParser::getAddonHtmlView() JROOT/components/com_sppagebuilder/parser/addon-parser.php:434
The list goes on....
https://cmtekwerx.com/dream/home