In addition to better apps, we need more apps in general to foster competition. If there was even one more Android and iOS app in active development it would be better for the community.
On the backend, they need to fix discoverability. Specifically search and link handling.
Sites like browse.feddit.de and Lemmyverse.net are fantastic resources that should be integrated into each instance's search capabilities. It should show all communities across all crawled instances whether they are blocked or not. Just display a flag that says blocked by your instance. The more transparently universal search is integrated the better for user understanding of the fediverse.
On the link handling front, when you use the ! Command to trigger community link auto insertion it makes something like:
[email protected] and hyperlinks it to https://homeinstance.tld/c/communityname
There is already a way to make universal links that has been discovered. Instead of the hyperlink, put (/c/[email protected]). This makes it so no matter what instance you have an account on, the link will always open the community in your instance, where you can then just subscribe. No need to copy the URL or community name back into your home instance nonsense.
Using my PlayStation 5 community that I mod as an example, here is an example of the current link handling (if you don't have a Lemmy.ml account this will kick you out of your home instance):
And this is how it should work in the Universal Link Format (this should keep you in your home instance):
For apps (at least for Jerboa which is what I use), neither of these links work properly. The first kicks you out of the app into the web browser, the second links you to a random other discussion. At least it work on the website.