This is not the canonical page

This page exists, but it tells search engines to index a different URL in its place.

What a cross-URL canonical does

A rel=canonical pointing at a different address is an instruction: treat that other URL as the real one and fold the ranking signals into it. It is the right tool for syndicated copies, parameter variants, and print versions. Used on purpose, it prevents duplicate-content problems before they start.

When it goes wrong

It becomes a real problem when a template hardcodes the homepage, or a staging domain, as the canonical for every page. Now the whole site tells search engines that none of its pages should rank on their own, and they should all defer to one URL. The pages drop out of results with no error anywhere, which is why an audit reports every canonical that points away from its own page.