Here is some additional detail from my investigation of Walks Around the Midlands. I looked at it using Kindle apps on iOS, Android, Fire, and PC. It is in Kindle Unlimited and available in the Amazon US store at:
https://www.amazon.com/dp/B08TVWQNML
Under iOS the book downloads in azw4 format (aka MOP). That format is a variant of MOBI that has long been used for print replica books. It contains a PDF that is only used to render page images, not for any other functionality. (kindleunpack can be used to extract the PDF from a MOP file.) MOP format also includes a simple table of words with the coordinates where they occur on each page. This allows for highlighting and annotations, but there is no provision for links as far as I can tell.
Under the other platforms the book downloads in the much newer print replica variant of KFX format generated by Kindle Create. Internally it has several PDF files each containing around 20 pages of the book, also used only to produce page images. This format has additional content coded in a way that is similar to fixed layout EPUB, allowing more functionality including links and pop-ups.
Some of the links work and some do not. As far as I can tell links that are not at the start of a block of text do not function. There does not appear to be anything wrong with the internal coding of those links. I assume there is a bug in the KFX renderer causing them to be currently non-functional.