But you mean here to keep the horizontal scroll, limit to like 5 entries, then a more button, right? This would also mean that suddenly all categories appear which could fill up the screen... couldn't that end up being too much?

Yes that's exactly what I mean. They might indeed fill the screen, which is the whole point if you have a lot of cats and want to see what you've got, or select several at once.
It would need an enhancement which is missing on the filter screen (but could usefully be added there as well) and that is when the full list is visible replace the more button with less which would collapse the list back to the otiginal howevermamy.

Originally posted by @rogercreagh in #847 (comment)