To fix those issues, you need to add the internal links to the webpage from other content on your website.

You can use Ahref to find the broken website for link building.

Yes, external links do matter in search engine rankings. Google considers external links as an alert of a website's credibility and authority. High-quality, relevant external links can boost a site's ranking, while spammy or irrelevant links can have a negative impact on its search engine visibility.