Note that sometimes in order to make "CTRL-1" or "CTRL-~" after you have started navigating through the Google slides, you need to click here at the bottom and then press "CTRL-1". Once you are scribbling, all commands work normally until you press "CTRL-~" and then Google slides seems to snag the keyboard from within the iframe. Kind of like shooting off-screen to reload in a video game. Note the black div just below the slide - that is a good way to have a subtle place to click outside the iframe.