But the main issue I can not add to index all pages due I do not know which not in the index.
Are you saying you wish to ONLY put pages/posts in the sitemap that have not yet been indexed? That’s not a good idea. Just leave ALL pages and posts in the sitemap. The option to exclude posts/pages is only there for cases where you are using an SEO plugin to add the robots:noindex tag on certain pages, or maybe only for pages that really have no value for search engines like cookie/legal notice pages (note that without the noindex tag they still might end up being indexed).
Otherwise, it’s best to have them all in the sitemap.
This is useful for Google (each page/post has also the “last modified” info which tells search engines to come back and index the changes) but for you too: you can then compare in the Search Console (webmaster tools account) how many of your pages/posts are indexed and how many are still waiting…
I do not understand why the sitemap does not work and not all pages in the Google index.
But you cannot force Google or any other search engine to come and index pages that are not indexed yet. You can only continue adding great content and build a better site, worth the extra attention from search engines.