I don't check this forum that regularly, so you're kind of lucky I see this. It's best to open an issue on the M5ez github.
As for your question: ez.buttons.poll() should return the key pressed, or an empty string if nothing is pressed, so you are presumably calling it from inside a loop? If you have nothing else to do in that loop and just want the the code to wait for a keypress, use ez.buttons.wait() instead. Let me know if this was not the issue, and in that case maybe show the code.