In version 1.86.2 on linux (i dont know whether it is matter) The system keybinding for toggle between the editor, the terminal and side bar is F6 and Shift+F6 for reverse toggle.
In more details:
{"key": "f6","command": "workbench.action.focusNextPart"}{"key": "shift+f6","command": "workbench.action.focusPreviousPart"}