still doesn't work, and i'm using Firefox
I tested on Firefox and I had the same issue as you. But the new option fixed the problem for me.
Please make sure you checked the “do not require ctrl/cmd” radio button in the Petaporon’s settings (top-left corner button). Then reload the page (make sure the option is still set after reloading. Petaporon store the settings in the browser’s local storage).
Only press Z to cancel (ctrl+Z will probably still conflict with Firefox, so Petaporon will not receive the keystroke). Similarly, only press X, C and V to cut, copy and paste selection of notes.