When you’re displaying the “full content” option, this is fairly common in displaying a classic blogroll. The way WordPress is setup, is you’re supposed to use the
tag within your post where ever you want it to be cut off over in the blogroll.
Alternatively, WordPress does not process shortcodes in
the_excerpt function. This is nothing specific to the theme. So unless you want to add this functionality via customization, this is not going to be possible.
I suppose you could do it theoretically from your Child theme’s
functions.php like this: