No canonical tag
canonical_missingShort answer
Nothing is broken. A canonical is optional; Google chooses one on its own. Add a self-referencing canonical if the same page can be reached under several URLs (tracking parameters, www and non-www, http and https, trailing slashes) so Google consolidates them to the one you want.
Why it matters
Google determines a canonical for every page whether you declare one or not. Declaring it matters when duplicates exist: without a canonical, Google may pick ?utm_source=newsletter or the non-www variant as the canonical and split your signals between versions. With a self-referencing canonical on every indexable page, every duplicate points at the same place. This is informational: it never lowers your health score.
How Glimana detects it
The rule fires for an indexable page returning 200 with no canonical in either the HTML head or the Link header.
How to fix it
Yoast, Rank Math and most SEO plugins output a self-referencing canonical on every page by default. If it is missing, the theme's wp_head() call was removed or the plugin's canonical feature is disabled — turn it back on.
Themes include <link rel="canonical" href="{{ canonical_url }}"> in theme.liquid. Restore the line if a customisation removed it.
Output <link rel="canonical" href="https://www.example.com/path"> with the absolute canonical URL inside <head>, on every indexable page.
How the fix is verified
Re-crawl after marking the task done; the task closes when the page declares a canonical.