Hi teitbite,
If you can access the "Layout" sub-section from Layout/Plugin menu, then you should see the option regarding adddthis/addtoany (according to the documentation).
I can only access the menu item "Layout & Plugins" - here, there's two "tabs" - one being Plugins (that is the first one shown), the other tab is "Layout" and nothing happens when I click this. I have used two different browsers, straight aftetr logging in - same issue, no difference.
The "addthis/addtoany" are buttons on the top of the comments-section, to share with others.
For now, I have disabled the system plugin "System - JA Comment" because it breaks the backend filtering system, and breaks the option to install (hence, also to update) Joomla extensions.
Try re-enable it (shortly, please), and you should see these buttons when logged in on the pages that have comments enabled (one being FAQ/OSS (https://mentalstyrken.dk/faq-oss)).