Unable to have image attachment page for subdomain…

On a main domain, inserting an image will produce:
this into the post, but…
on a subdomain, inserting an image will produce:
this

The only way for me to recreate the same result enabling an attachment page for an image is if I manually add the “attachment wp-att” code to replace the “href=” code (which skips creating an attachment page link).

Is it possible to have attachment pages automatically created for inserted images on a subdomain? If so, what needs to be done in order to accomplish that?

Please be specific with help and don’t leave out any steps, including whatever the filenames may be which need editing (and also where they are located).

I greatly appreciate whoever may help me.