Background
The grid view of the Media Library (including the Media Modal) has supported infinite scrolling for a long time, where attachments load automatically as you scroll instead of behind a Load more button. That behavior was controlled by the media_library_infinite_scrolling filter, which defaulted to false since WordPress 5.8 due to accessibility, performance, and usability concerns (#50105 / r50829 / #40330). As a result, infinite scrolling was effectively off for everyone unless a plugin or theme opted in via the filter.
The Load more button has long been a friction point for users managing large media libraries, and the smoother infinite-scroll experience was hidden
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