Hi @brettwray,
I hope you are well today and thank you for your question.
I have tested it on my test site and it’s working fine for me using latest version of Shapely theme as displayed.
If you can’t set the featured image for the post then this can be due to plugin conflict on your site so please try temporary deactivating all plugins and see whether everything works fine and then enable the plugins one by one to see which plugin is conflicting if any.
If you want to display the featured image on single post page then try using the child theme solution shared in the following topic.
Best Regards,
Movin