in gnome shell when several applications are open in different workspaces i use applications switcher Command + Tab (or Alt + Tab in a PC) to active/switch to the app/workspace i want to use.
is it possible to terminate an application within the application switcher, like in the mac environment with Command + Q (or Alt + Q in a PC) instead of using the window control icons or add this function somehow?
There is no default shortcut for that. The Power Alt-Tab extension should fit your needs, though.
According to the author, the extension: