Disable multi cursor functionality

Un-check Selection->Column Selection Mode

You can remove the keyboard shortcut(s) that trigger this functionality.

Click on the gear on the bottom-left corner of the window and choose "Keyboard Shortcuts" from the menu. Type "Add Cursor" into the "Search" box and it shows only the commands that contain "Add Cursor" in their name.

Right-click on each command that add a cursor and has a keyboard shortcut associated and select "Remove Keybinding".

Also search for "Multi-Cursor". It could return the command "Toggle Multi-Cursor Modifier" that is associated to a combination of modifier keys (one or more of Ctrl, Alt, Shift). If such a combination of keys is pressed when you click in the editor window it adds a new text cursor at the click position. You should also removed these key bindings.

Set this settings in editor settings :

"editor.columnSelection": false,