I think he is talking about the semi-transparent arrow mid way down the left side. This is the indication that there is an app(s) in slide over waiting. It may or may not be the chrome window showing in the bottom thumbnails.
You can swipe from the left to reveal the app, then used the three dots at the top to close the app. If more than one app is in slide over, you'll need to close them all.
Alternatively, if you don't want any of the multitasking features, you can now go to Settings > Multitasking and Gestures to turn off all the multitasking features. Keep in mind this does mean all of them. You won't be able to view more than one app at a time. That includes the picture in picture feature that some apps like Youtube have. You need to be on the latest iPadOS version to do this.