My wife has a Samsung S9 Plus. Recently when browsing on Chrome, if she touches the top right corner of the edge (very close to the 3 dots to access settings), a popup displays showing various videos and adds. When hitting the back button, a pop displays asking "Want to leave fun now?". Options are leave or stay and an option box to not show the message again.
I've cleared all browsing history, and cleared the cache in the phone settings. I've run Bitdefender mobile protection and Malwarebytes. Neither program found any issues.
I have the same phone, but do not have the same issue, so I don't think it is a new "feature". I'm guessing it is some form of malware, but can't find any info on it or a way to remove it.