Cmd+Q quits the running application i.e it will close all the open windows of the app and quit the app. On Windows Alt+F4 is for "close the window" (macOS equivalent of Cmd+W) or to be more precise it sends the "WM_CLOSE" message to the window and the program can do whatever it want to do with that message, the default behaviour of that message handling is to close the window. Closing a Windows doesn't necessarily means quitting the app. If you have multiple Notepad windows you will have to do Alt+f4 on each one of them to actually "quit" notepad. Some Windows app have a quit shortcut like "Ctrl+q", if you press that on Notepad, it will behave like macOS Cmd+q.
On another note, the first keyboard shortcut I change on any Linux installation is the "Alt+f4" one, it is such a painful key combination to press :)
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Cmd+Q quits the running application i.e it will close all the open windows of the app and quit the app. On Windows Alt+F4 is for "close the window" (macOS equivalent of Cmd+W) or to be more precise it sends the "WM_CLOSE" message to the window and the program can do whatever it want to do with that message, the default behaviour of that message handling is to close the window. Closing a Windows doesn't necessarily means quitting the app. If you have multiple Notepad windows you will have to do Alt+f4 on each one of them to actually "quit" notepad. Some Windows app have a quit shortcut like "Ctrl+q", if you press that on Notepad, it will behave like macOS Cmd+q.
On another note, the first keyboard shortcut I change on any Linux installation is the "Alt+f4" one, it is such a painful key combination to press :)