Hi @ublien and @gentile
If there is no shortcut key setting available to close a viewport (other than the standard Windows Alt-F4), there is possibly an alternative solution.
There is a free application “AutoHotKey” available from autohotkey.com and a script could be written that would remap the Esc key to Alt-F4 if KNIME is the active application.
View ports all get given different windows titles (depending on the node) and KNIME is java-based and so there is limited native-windows information available to AutoHotKey in terms of identifying if the current window is in fact a View Port, but I have only been able to check the the current active isn’t titled “KNIME Analytics Platform” (as we don’t want random presses of Esc shutting down KNIME all the time 
What this means is that any KNIME dialog would be closed if the Esc key is pressed, which may be acceptable but I don’t know for sure that this won’t cause problems.
Anyway the AHK script to achieve this is:
/* Auto Hot Key script to remap Esc into Alt-F4 in KNIME.exe
Gives the user the ability to remap a key Esc in this example) to work as the standard Close Window key
Script written by @takbb Brian Bates - 20 Nov 2021
This script is free to use for any use
Use at your own risk!
To use this script, install AutoHotKey - available from autohotkey.com
Place it in same folder as a copy of AutoHotKey.exe
rename AutoHotKey.exe as KnimeRemapEscToAltF4.exe
(i.e. the same name as this script, but with .exe extension)
Ensure that both
KnimeRemapEscToAltF4.exe
KnimeRemapEscToAltF4.ahk
are in the same folder, then run KnimeRemapEscToAltF4.exe
Run either at Windows Startup, or manually run it when you are running Knime.exe
*/
;TrayTip, AutoHotKey, Looking for KNIME Analytics Platform - Esc->AltF4 Remap , 16
SetTitleMatchMode 3 ; window title equals
loop {
#IfWinActive ahk_exe knime.exe
; specify the Key to be remapped here.
; for list of keys see AutoHotKey help at https://www.autohotkey.com/docs/Hotkeys.htm
Esc::
; if hotkey has been pressed, get the current active window title as we only want to turn the key
; into Alt-F4 !{F4} in autohotkey terminology, if it isn't the main KNIME window that is active
; Unfortunately all viewports in KNIME have different window titles so we cannot easily do this based
; on it only being a viewport window, or config window
WinGetActiveTitle, Title
activeTitle=%Title%
if (activeTitle != "KNIME Analytics Platform")
{
; only convert Esc to F4 if the current active window is not the Main KNIME application window
Send !{F4}
}
return
}
Instructions are basically this:
(1) download and install AutoHotKey
(2) Copy the above script into notepad and save the file to a folder as
KnimeRemapEscToAltF4.
txt
(3) Rename it to KnimeRemapEscToAltF4.
ahk
(4) From your autohotkey installation folder (probably C:\Program Files\AutoHotkey), copy the AutoHotKey exe appropriate to your windows system (probably AutoHotkey.exe) into the same folder as your KnimeRemapEscToAltF4.ahk file.
(5) Rename the AutoHotKey exe in this folder as
KnimeRemapEscToAltF4.exe
Make sure you have “File name extensions” visible, so that you don’t end up with a file called KnimeRemapEscToAltF4
.ahk.txt. It should look like this

(6) Run KnimeRemapEscToAltF4.exe
(7) Open a viewport in KNIME.
(8) Press “Esc”
(9) Enjoy!