First of all, one million is a lot of URLs to get indexed. If the content is indexable (whether scraped, AI-generated, or human-written, it must be indexable), otherwise, it will not be indexed. If the content is indexable, you can invite crawlers by building backlinks.
GSA SER and Xrumer forum profile blasts will help, but of course, you don't have to import all one million backlinks, as it will overwhelm the software and cause memory issues. Therefore, try to build backlinks to at least 10K - 15K links using software like GSA. Then, the URLs will start indexing and new ones will begin to appear automatically as they are supposed to.
If you have one million URLs, at least 10K should be indexed by now.
I own a doorway website (used as a T2 to my main site) built entirely with GPT. It has 100K pages, of which 77,000 are indexed, and it is run entirely by GSA blasts.