Here is a simple solution on how to close apps on your iPhone 13 series. Seeing there’s no button the game has changed but luckily apple has a easier solution.
Models this works for are
iPhone 13
iPhone 13 pro
iPhone 13 mini
iPhone 13 pro max
Also for those trying to figure out how to close apps on their iPhone 12 this covers
iPhone 12 / 12 pro / 12 mini / 12 pro max
Not only there it also works if you want to know how to close apps on your iPhone 11 series
iPhone 11 / 11 pro / 11 pro max