The default Toggle explore side bar shortcut keys Ctrl + B, but this conflict and Vim shortcuts, workarounds:
File > Preferences > Keyboard Shortcuts，
Input ctrl + m, select Default match, right-click to select Remove Keybinding.
Then enter Toggle Side Bar Visibility, right-click to select Change Keybinding, you can enter Ctrl + m.
Later on with Ctrl + m to open / close explore side bar.