In case anyone is confused about this:
Here are the instructions in the Cubase 9.5 Pro manual:
“To show or hide the Regions, click Set up Window Layout on the toolbar and activate or deactivate Regions.” (The manual says this on page 461.)
What’s not stated clearly is that there is more than one Set up Window Layout button. You need to click the one that’s in the top right corner of the audio Editor window.
I hope that helps.