Start up your iPad, then double click the home button. You will see all the open apps shown as thumbnails. Swipe the thumbnail picture of the apps upward and that shuts them down — no problem doing that. Leaving them open just reduces the time it takes to launch the app, which isn’t much. I make sure I do this after visiting my bank or performing any financial transactions. In fact banks tell you to close your browser (Safari) after visiting your account, and relaunching Safari before going to another website.
BTW, you can always log out of your apps, it just takes longer than swiping up. Go to your account in the app and select “log out.”
Direction with pictures here -
https://www.imore.com/how-force-quit...-ipad#iphone-8