I see the same issue here @Ann Bens on my iPhone 12 Pro Max. Whole screen loads of unnecessary whitespace. Lots of scrolling required to see content. All browsers.
I'm seeing similar symptoms on my Iphone 11 Pro / IOS 18.2, with Safari, Chrome, and Firefox, with all the Lightroom Classic forums. Not only is there large amounts of unnecessary white space after the first posts, as shown in the screenshot above, but comparing the posts shown on the Iphone with what's shown in a desktop Web browser (e.g. Chrome), at least one or more posts simply aren't displayed on each page of posts.
I just updated to IOS 18.3.1 and I don't currently see the bug. It's been intermittent in the past month, so if I see it again, I'll be sure to update here.