Heya! Your friendly QA Tester here.
I just finished a run and, after pressing "New run", tried to go back to the main menu to check my collection only to notice that there's no way to go back. There's no button and ESC doesn't work either.
Right now, you need to restart the game or go into a run and then to the main menu.
Seems like a minor oversight, but I thought I'd let you know.
Hope it helps!