I'm trying to send Alt+Tab to my remote buddy but it does Alt+Tab on my local machine.
GNU/Linux, Fedora, Xorg, not Wayland.
Alt+Tab should be trapped and sent across to the remote side if your mouse is inside the bounds of the call window (if it's full screen, then your mouse just needs to be on that screen). Can you confirm that Alt+Tab isn't being sent over regardless of your mouse position?
Can you also share the output from xinput in your Terminal? That may shed some light on what we may need to do to fix this for your keyboard. Thanks!