I don't know what happened with my previous response, but I'll reply again.
I have disabled Yoast SEO plugin and suddenly dozens of pages with images attachment started appearing on google when I type my site name.
But the original posts still are not being indexed.
Today I installed a WordPress plugin to redirect these image posts to the original post and I hope to have the problem solved in the next days.
Unless that Google is so evil or if there's another weird problem in my site.
Google Search Console is also showing hundreds of extra pages being indexed as follows in the image.