The book demo started from a .featured span and moved around its article. Your repair-café card has one extra layer: the .featured-tool label is inside a .tool-row, and that row sits inside an <article>. One step up should find the row, while closest("article") must find the outer card.
On an unrelated music-card page, the same route could look like this:
const tag = document.querySelector(".album-tag");
const row = tag.parentElement;
const name = row.children[0];
const album = tag.closest("article");
name.textContent += " (recommended)";
album.dataset.highlight = "yes";
In your page, the first child of .tool-row is the tool name. Append ** (available)** to it and mark the article with data-featured="yes". Observe the green border in Preview. Keep the second card untouched.
.featured-tool, use parentElement and its children[0] to append (available) to the tool name in the same row..featured-tool, use closest("article") to set data-featured="yes" on its enclosing repair card, not on the inner row.