Thanks to Semaniel's Youtube video and feedback, I realized that End Turn button looks too similar to Undo, making it easy to mis-click.
So I added a gradient texture around End Turn button, which makes it looks different. Also, just as End Turn text, this texture is painted red when there are cards in hand that are going to be discarded (i.e. non-Retained cards). Which also helps to make fewer not-Undo-able mistakes.
Also, Tutorial screens now support Escape button. Before that, Escape button was consumed by their parent screen, and it looked weird.