To test you need to:

    Remove/backup your input settings: ~/.local/share/krita/input/kritadefault.profile
    Restart Krita

Now you have different ways to zoom your canvas:

    Ctrl+Space+LeftBtnDrag --- zoom relative to center
    Ctrl+Alt+Space+LeftBtnDrag --- discrete zoom relative to center
    Ctrl+MiddleBtnDrag --- relative zoom
    Ctrl+Alt+MiddleBtnDrag --- discrete relative zoom