I use Audacity 2.1.2 on a Win10 machine.
I would like to know if it possible (in the context of multitracking edition) to select a part of a track and to revert the selection vertically in order to blank all track but the one selected (on the vertical selection))
A picture is better than a long speach :
I would like to blank all tracks in red by selecting the non red track
You can make the selection in one track, then “Edit menu > Select > In all tracks (Shift + Ctrl + K)” to extend the selection to all tracks, then Ctrl+Click in the panel on the left end of a track to toggle the selection off for that one track. This will (quickly) give you all tracks selected except for the track that you toggled to “not selected”. Then press Ctrl+L to silence all selected tracks.
That might be a new feature in Audacity 2.1.3, which hasn’t been released yet (I’m using the alpha version).
In current versions you can toggle the selectedness of the “current” track (the track that has “focus” as indicated by having a yellow border to the track) by pressing the Enter key. The “track with focus” is usually the last track that has been clicked, and you can move focus up/down to other tracks by clicking the up/down cursor keys.