Hi 🙂
Thanks for posting.
Please, remember not to edit any files in the theme directory, the entire directory is overwritten during theme updates so it’s best to make changes, if required, in a child theme.
The easiest solution for adding page templates to posts is to use the following plugin: https://wordpress.org/plugins/custom-post-type-page-template/. Once installed and activated, go to Settings > Custom Post Type Page Template
and activate the posts option. Then, edit any post and at the top in the right column you’ll be able to choose any of the theme’s page templates.
Hope that helps.