Alt+F4 kills the process.

Nope, Alt+F4 is the close window shortcut.

This is even visible in the OS-controller Window Menu - hit Alt+Spacebar in any window of any app, and you'll see the Window menu appear, which will include an option for Close (the current window), showing that the shortcut for it is Alt+F4. This is even true for modal dialogs (if they are real Windows modal dialogs).

Weirdly enough, Alt+Spacebar, then clicking close only closes the window (minimizing to the tray), but just hitting Alt+F4 kills the process.

You mean for Discord I assume? That is strange indeed - though of course Windows has always allowed apps to modify any kind of behavior they want (for better and for worse).

No it doesn't.

If I open blender and hit 'Render Image', a new Window will open with the rendered image. This does NOT spawn a new process. Hitting Alt+F4 on this window closes the window. This does NOT kill a process.

Alt+F4 asks the window to close. If it's the main window, this will by default terminate the message loop, shutting down the application. But the application is free to handle the message whatever way it likes. Asking for confirmation, ignoring it, or closing the window without terminating the process.

guys i dont know why im getting downvoted - on my windows 10 machine, newest discord version -> alt+f4 kills the process and x-ing the app does not.

Except for Discord, which actually closes the entire application on Alt-F4 instead of just the window.

Huh. You are right. Alt+F4 closes the application, clicking the X closes the window. Kinda inconsistent.

Alt-F4 invokes different processes than the X button does. The X button is more akin to CTRL-F4.

Nah, they both send WM_CLOSE to the window. The actual problem is that Discord uses its own non-native window frame and reimplements the X button differently than they handle the actual close event.

Alt+F4 closes the window, clicking the X causes the window to hide, not close.

Alt-F4 closes the window for me on Discord, not the app. There's a setting for that I suppose.