I've seen people suggesting improvements to sign-up which mostly amounts to hiding technical language (servers, instances, fediverse) and adding clearer signposts. I'm also seeing discussion on GitHub around UI improvements to the website as well as native apps.
Add a way to 'browse' communities. A way to discover communities by navigating different categories instead of just search. Search often finds no hits if you don't know what is there. Search is liked by text thinking users, but fails badly for visual thinking users.