Increasing number of "Crawled currently not indexed" for a huge website

I have a website with millions of pages, it's like a database where the majority of onpage content is automatically generated and the only bits of unique content are a few lines. I know this isn't helping me since Google sees it as duplicate content and this leads to Google choosing a different canonical or not indexing my pages.

However, it would be impossible to add unique content to thousands of pages. Is there any way I can fix this? Or any alternative I can investigate to stop Google from deindexing my pages?

Thanks