Article page error help

So i've set up a blog on my site, however, the article pages are showing errors and i simply don't know what any of it means. Does anyone know what might be the issue?

A side question.. I've noticed the sidebar in my blog only contains a text widget, whereas the sidebar.html.twig file shows that there should be several other widgets, such as 'Related Posts' and a search bar. What could be the reason those are not showing up too?

My websites blog: http://www.thecabinetshop.co.uk/blog

Thanks.

The issue looks like coming from you having the Breadcrumbs plugin enabled, but not installed. This can happen if you install and enable it, but then uninstall it.

The widgets are provided by plugins, as you can see in the Twig directly (it will check for some plugins to be enabled). Namely, Related Pages and Simplesearch plugins. Install them and they will show up.