"item" in Bootstrap 3 is now "carousel-item" in Bootstrap 4.
Here are some other differences...
http://www.quackit.com/bootstrap/bootst … trap_4.cfm
Check out a rough draft of my Bootstrap Carousel which includes CSS Animate and JavaScript add on that gives control of delay and duration.
http://gluexp.coffeecup.com/index.html
Bootstrap 5 CSS Grid.