Je cite la réponse, qui m'a sauvé la vie plusieurs fois, et dont le ton prête à sourire :

OMG REALLY!!  YOU CAME HERE ASKING FOR HELP AND THEN DIDN'T EXPLAIN HOW TO FIX IT!!!

THE SECOND PERSON CAME HERE WITH INSTRUCTIONS AND DIDN'T ANSWER THE QUESTION HOW TO TURN IT OFF!!!

WHAT IS WRONG WITH YOU PEOPLE!?
Toggling between line and column selection modes

To toggle between the line and the column selection modes, do one of the following:

    On the main menu, choose Edit | Column Selection Mode.
    On the context menu of the editor, choose Column Selection Mode.
    Press Shift+Alt+Insert.

BURIED ON THIS PAGE: https://www.jetbrains.com/help/phpstorm/selecting-text-in-the-editor.html#column_selection

 Google searches that were unfruitful: webstorm free spacing (visual studio/MSWord calls it free spacing), webstorm turn off multi-caret, webstorm turn off column selection.  How is anyone supposed to find this setting?