Programmatic SEO Pages Not Indexing: 135/150 Pages "Duplicate Without User-Selected Canonical"

I’ve looked up this error, and it seems to mean that the content is too similar, so Google is treating them as duplicates and assigning them to a single page rather than recognizing all 150 pages as different. I took one of these pages and made significant changes, adding 2-3k words of content and altering the meta description and title. However, after requesting indexing again, it still shows up as a duplicate.

Any ideas on what might be the problem? Could there be a technical issue with the structure of the pages that’s causing this?