Previously, there was a limit of 5,000 projects per Project Web App (PWA) site. Now, you can create up to 30,000 projects within each PWA site. In addition to creating more projects, you can also have a project site for each of your projects. With this update, we’ve moved the site creation settings into the Enterprise Project Type (EPT) so that the project site creation can be defined at the EPT level.

View Brian Smith’s blog for additional information regarding Site Creation Settings

https://blogs.technet.microsoft.com/projectsupport/2017/06/12/project-online-what-happened-to-my-site-creation-settings/