Consolidate duplicate URLs - Search Console Help
When Googlebot indexes a site, it tries to determine the primary content of each page. If Googlebot finds multiple pages on the same site that seem to be the same, it chooses the page that it thinks is the most complete and useful, and marks it as canonical. The canonical page will be crawled most regularly; duplicates are crawled less frequently in order to reduce Google crawling load on your site. Google chooses the canonical page based on a number of factors (or signals), such as whether the page is served via http or https; page quality; presence of the URL in a sitemap; and any "rel=canonical" labeling. You can indicate your preference to Google using these techniques, but Google may choose a different page as canonical than you do, for various reasons. Google uses the canonical pages as the main sources to evaluate content and quality.
Related: Redirects (301, pagination, next/prev, canonical) & 404 Errors