I am used to use ctrl+shift to change keyboard layout. I found how to do change keyboard layout :
However, I can't set crtl+shift, for example, I can set only ctrl+tab or ctrl+c or ctrl+shift+w etc but can't only ctrt+shift. How to do it?
Looks like you are running the Gnome Desktop Environment. If so, you can do this with the Tweak Tool. Search for and run the tweak tool, select Typing>Switching to another layout and tick the box for Ctrl+Shift.
A thing that happen to me once is (for my work) I needed to edit a field on a web page with Ctrl+Alt+Shift. This combination of keys was working on a Doze machine but not on a Nux machine. The culprit was the default keyboard layout itself. I changed it. So if you can change your defualt keyboard layout.