I think the most downgrade thing is the reactions/emojis button, the window can't load all my favorite custom reaction packs as it's narrow and static. It also sacrificed favorite emojis for "frequently used".

I used to like how more control over Relays I had instead of everything fitted on "app relays", like inbox and outbox (this help a lot during bots times)

The feed used to look better and prettier before and it seems it takes more time than before to load stuff too now.

IDK if it's going to be useful but I appreciate you asked.