I'm using the latest version of the Dawn theme installed from the theme store. In the theme customizer, when I change the dropdown menu at the top to "product" or "blog post" (article) those options are greyed out and I can't make edits to those templates.
According to the code at https://shopify.dev/apps/online-store/verify-support#requirements, both of those templates have support for sections everywhere and contain @app blocks, so it ought to be possible to add my app blocks to them, but I can't even edit them.
Anyone else having similar problems?
Try and download a new copy and check that.
Beyond that you may need someone to take a look at the store theme in the admin.
Try clearing your browser cache, or private browsing mode, or a different device to rule out your current computer setup.
If that doesn't do it contact me at firstname.lastname@example.org with store url and i'll send a request to take a look.