In many common programs, control z is to undo and control y is to redo an action. However, in blender, the shortcut is control+shift+z. I’m not sure whether this was because of control y already being a shortcut, but I can’t think of something in Blender that uses control y. My guess is that the Blender Developers weren’t really familiar with the control y shortcut, but they did know that shift is often used to change a keybinding. And then they made the redo shortcut control+shift+z. I just don’t want people to be confused as to why they can’t control+y to redo in Blender.
Some few apps use ctrl+y to redo, but control+shift+z is still the most popular shortcut for it.
There is no CTRL+Y anywhere on my Mac as far as I can tell… But there is CMD+SHIF+Z (default MacOs option), and/or CTRL+SHIFT+Z for some apps, for redo.
Cheers, Clock.
PS. Welcome to Devtak @NathanMillerson!