Hi and welcome to the forum.
Perhaps rounded corners should be an option. My personal preference would be no rounded corners.
Not all applications respect the Bottom Corners to be rounded in the new Gnome.
You can do this easily on other Desktop Environments but... As it is, the Zorin Themes included rounded corners for the apps that do respect them. VLC is a QT app, not a gtk app.
There not much that can be done for non-GTK apps other than switch maybe to a GTK media player.