Thanks for the help, Timo! It turns out the skin was causing the problem(s). Now everything works and looks just fine. 😀

I haven't installed any extra extension that weren't in the original install package (I'm using MediaWiki 1.45.0-alpha).

Below is a screenshot of the search result page (sorry for the meta search term, btw). As you can see, there's no option to create the missing page. Just a "No result"-messsage.

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