We have a undo keyboard shortcut but no redo one. I know Jupyter doesnt have a redo keyboard shortcut in command mode, but their CTRL+Y shortcut works.

To make matters a little worse, on Mac, Cmd+Shift+Z, which should be redo acts as undo as well, so as you try to fix your mistake you're losing more and more work :(
OMG!!! Why my cell disappeared after Ctrl + Z. How can I recover them?
@zhqu1148980644 We'll look into and fix this issue. There is a known issue where undo may delete the entire cell if you have not run the cell yet, that we're woking on fixing. Thanks for the feedback.
'Z' is supposed to undo the last cell change. CTRL+'Z' is doing the same because we don't check for the CTRL key when a cell doesn't have focus.
I'm going to change it so you have to hit just 'z' when a cell doesn't have focus
And shift+z is redo (like Jupyter Lab has)
Validated