Just creating this post to share my issue and how i fixed it. We had an issue on our self-hosted ghost instance that left the sitemap-posts.xml file missing in the myblog.com/sitemap.xml file. We were running the latest versions of ghost (so at this post date it was 5.59.2). After checking our config.production.json file and routes.yaml files we could not find why the sitemap was missing and our google skills were getting us no results, so we decided to pray and hope it could be fixed by rolling back version. We found out that the sitemap-posts.xml file was present again in version 5.20.0 so we will stick with this one.
Hope this will help some people having the same issue as we did.