My system is Ubuntu 20.04.2 LTS, Gnome version is 3.36.8.
I am going to Settings -> Keyboard Shortcuts.
Some keyboard shotcuts can be changed, while some are not.eg; "Switch to next input source" (for language switching). I press it, the pop up window says "Set Shotcut". If I press e. g. Alt+Tab, the system allows me to do that.
However if I want to do Alt+Shift (which is the classic one for language switching), the system does nothing.. Neither works Ctrl+Shift, Ctrl+Alt etc.
As far as I see, Alt+Shift is not assigned to any other other command. Please help..