With the new update of Premiere Pro (version 23.4) horizontal scroll on the timeline hardly works at all. When I use a two finger swipe on my trackpad to move the timeline left or right, it normally moves very smoothly and moves long distances quickly. But in version 23.4 it hardly moves, and I have to push down hard on the trackpad and do really long swipes to initiate a (weak) scroll.
I ended up reinstalling version 23.3, and horizontal scroll on the timeline now works perfectly again.
I hope this will be fixed with future updates so I can always have the latest version.