When opening a modal, the backdrop should fade in (as per the example in the Bootstrap docs: https://getbootstrap.com/docs/4.0/components/modal/#live-demo), however it just appears immediately.
From looking at the code, Bootstrap creates its backdrop with the ‘modal-backdrop’ and ‘fade’ classes, adds it to the DOM, and then adds the ‘show’ class, whereas in ng-bootstrap the backdrop is created with all three classes already on it.
Link to minimally-working StackBlitz that reproduces the issue:
https://ng-bootstrap.github.io/app/components/modal/demos/basic/stackblitz.html (this is the one from the documentation for the modal component: https://ng-bootstrap.github.io/#/components/modal/examples)
Versions of Angular, ng-bootstrap and Bootstrap: