In the Site Audit Tool, under the Overview and Progress tabs in the Errors graphs you can see:

The Site Audit Tool's Overview and Progress tabs display graphs that track the number of errors identified during each individual crawl of your website. This historical data allows you to monitor trends, assess the impact of changes, and understand your site's health over time. It doesn't show errors only on the main page, but across the entire audited site. While the tool provides real-time updates during an active crawl, the graphs themselves represent the completed results of each distinct crawl, not a live, constantly updating count of errors.