Earlier quoted context omitted.
Hammerspoon can do this quite easily, just grab all the windows using hs.window.filter.defaultCurrentSpace:getWindows() and set each's frame to it's screen:frame().
Thank you for the tip, I'll to code the algorithm to do it myself. That's great ! On an other note: a tip on iOS and MacOS, when you make a voice recording then you can edit it and activate a feature with the top left wand icon which is going to clear up the sound. When it's a voice recording it's pretty amazing how well it works, in particular to remove the echo.
What I want to do actually IS the mission control mode where all the windows are resized to fill up the screen.
To close a window while in exposé mode, the easy solution is effectively to use BTT, creating a new gesture for example "3 fingers click" with the ctrl modifier. Then selecting the action "Close Window Below Cursor (Works in Mission Control)".
And this effectively close my window. An other tip here, still in mission control while the cursor is on a window, pressing the space bar displays it full screen.
One more thing: While doing COMMAND + TAB to show the open apps, pressing the bottom arrow key show all the open windows for this app, regardless of the space they are in. Really useful.