Users with low vision may use the zoom functionality of the browser to magnify the content of your web pages.
WCAG 2.1 requires that at up to 400% zoom:
content can be presented without loss of information or functionality, and without requiring scrolling in two dimensions
Zooming in effectively makes your viewport smaller so it's important that your pages are responsive.
It's difficult for an accessibility checking tool to verify this but an auditor will pick this up. There are no shortcuts to achieving this standard, just good responsive design.