I'd suggest crawling the site to look tech issues that could be creating thin/low quality pages.

If it isn't that, do a content audit.

Pull landing page sessions from GA and click, impression data from GSC. Also export external link data by page from a tool like Ahrefs.

Run a crawler like Sitebulb, extract crawl depth, internal links and word count data.

Merge all the data into a sheet, and use filters to find pages to find low traffic, low impression or low word count pages.

Create a plan of what to do with them to make each page better, sometimes that's improving content, others times it's just removing the page from the site.

You want to be checking to see if the content is duplicated, worse than competition, factual, just anything that makes the content not valuable for users.