I have some legacy code which I am trying to update from bootstrap 3.4.1 to 5.3.3. Upon upgrading, a modal in my application no longer appears and there's an error in the console. On investigating, it seems that some legacy code is trying to manually hide the Bootstrap $backdrop property:

var bsModalBackdrop = $(bsModal).data('bs.modal').$backdrop;
if (bsModalBackdrop) {
  bsModalBackdrop.addClass('hidden');
}

The error is that $(bsModal).data('bs.modal') comes up as undefined, whereas with Bootstrap 3.4.1 it contains an object like this:

{bs.modal: s}
    bs.modal: s
        $backdrop: S.fn.init
            0: div.modal-backdrop.fade.in
            length: 1
            prevObject: S.fn.init {0: div.modal-backdrop.fade.in, length: 1}
            [[Prototype]]: Object
        $body: S.fn.init {0: body.il-body.modal-open, length: 1}
        $dialog: S.fn.init {length: 0, prevObject: S.fn.init}
        $element: S.fn.init {0: div.il-modal.modal.fade.il-modal-sm.from-right, length: 1}

        bodyIsOverflowing: false
        fixedContent: ".navbar-fixed-top, .navbar-fixed-bottom"
        ignoreBackdropClick: false
        isShown: true
        options: {backdrop: true, keyboard: true, show: true}
        originalBodyPad: ""
        scrollbarWidth: 0
        [[Prototype]]: Object
    [[Prototype]]: Object

Has this functionality been removed, or replaced somewhere else? I've tried deleting the above code, but then the backdrop stays in place and I just don't get the error message. It seems my code does expect Bootstrap to have placed the bs.modal property on the element and needs to remove it.