The visibility property only tells the browser whether to show an element or not. It’s either visible (visible – you can see it), or invisible (hidden – you can’t see it).
The display property tells the browser how to draw and show an element, if at all – whether it should be displayed as an inline element (i.e. it flows with text and other inline elements) or a block-level element (i.e. it has height and width properties that you can set, it’s floatable, etc), or an inline-block (i.e. it acts like a block box but is laid inline instead) and some others (list-item, table, table-row, table-cell, flex, etc).
When you set an element to display: block but also set visibility: hidden, the browser still treats it as a block element, except you just don’t see it. Kind of like how you stack a red box on top of an invisible box: the red box looks like it’s floating in mid-air when in reality it’s sitting on top of a physical box that you can’t see.
In other words, this means elements with display that isn’t none will still affect the flow of elements in a page, regardless of whether they are visible or not. Boxes surrounding an element with display: none will behave as if that element was never there (although it remains in the DOM).