When using certain applications (such as the built-in "Screen Sharing" VNC app or VirtualBox) the command-tab key combination has unexpected/unwanted behaviors:
In Screen Sharing, when connecting to a remote Windows 10 machine, the command key acts like the alt key. Command-tab activates the Windows task switcher and doesn't activate the MacOS application switcher. Other MacOS command-key combinations are interpreted by MacOS (ie, command-up brings up Mission Control). I would prefer to have the command-tab bring up the MacOS application switcher and use alt-tab to bring up the Windows switcher.
When running a Windows 10 vm in VirtualBox, command-tab does bring up the MacOS application switcher, but it also acts as if the windows key was pressed in the vm (bringing up the Windows start menu).
I have seen similar behavior in other remote/sharing applications such as TeamViewer and Splashtop.
I use Karabiner-Elements for other key mapping needs, so a solution involving MacOS Preferences, the relevant application preferences or Karabiner would be preferred.