It doesn’t appear to be the theme that is the issue.
I created a test site. See https://joshuaallenshaw.com/test/. I make a post that, https://joshuaallenshaw.com/test/2020/01/09/hello-world/, that has the image you requested of the settings. This site is using the generic theme, so I added the php code blocks to the body. There is nothing there.
Some of the plugins on this site are network activated. Is it possible that a plugin is causing this issue? There are no plugins active that impact media or themes.