I was today years old, when I got to know about those key bindings. As a gnome user you may already know that it is all about workspaces. You’re supposed to use those workspaces instead of minimizing your running applications to a task bar. The conclusion is, there must be a setting or a shortcut to alt-tab on the current workspace. And there is.

Alt + Escape to switch between applications of the current workspace

Alt + ~ to switch between windows of the current application