I think it's some sort of layout issue. I don't see horizontal arrows in mine (11.0.2), either ... but if I click between Character and Applications, I can see the arrows briefly appear before the panel changes. @Peter any idea what's going on here?
I do have a vague impression that it vanished rather recently – perhaps after the latest Sonoma update.
(Vanished on two different Sonoma 14.3 machines here – different screen sizes and aspect ratios – so presumably not an effect of a setting on a particular device)