In Lemmy 0.19.4, scores were reworked. So that you could individually pick which score you like to see (upvote, downvote, total, ratio)
Before this this option its behaviour was to disable every score type. Now it just hides the "total". With Lemmy 0.19.4 they did a poll to see which scores are the most popular and should be the default. Upvotes + Downvotes won. So show_scores is now by default false.
Currently our setting division ('Account settings' vs 'look and feel') doesn't make much sense. But 'look and feel' is all the settings that are stored on the device. Thus apply to all accounts. Account settings are settings we retrieve from Lemmy and are different per account.
So that brings us to the listingviewmode. That shows the total_scores but since its disabled, it is hidden. I'll probably rework it so that it shows the upvotes if 'shows_scores' is disabled.
Gifs never worked in comments. Could never get it to work. But imageviewer should always auto play gifs regardless of the setting autoPlayGifs. So that's a bug I'll look into.
The setting is for controlling previews and icons/avatars.