BlackBerry Priv stock multi-tasking interface can be enabled in Settings
Now there is a solution to that problem thanks to Redditors. You can change the multi-tasking interface back to to the stock interface because you can use a hidden setting option. In order to change the interface, all you have to do is go to Settings → Display → Recent and choose the Rolodex option to get to the desired multi-tasking view. Problem solved!
Source: XDA Forums