The secret ingredient is enshittification.
What’s bad about discord?
It’s actually optimized for them. The goal is to get users to spend time and see ads etc. The UI is not made for us users.
The discord UI was great. And then they made it ugly and slow as fuck.
I’ve been using aliucord
For YouTube, use FreeTube, Tubular or LibreTube if you like native clients or Piped and Invidious if you prefer a website.
It’s best not to use Reddit at all, but if you need it for some reason, check out Libreddit or this site
Unfortunately not much can be done to avoid Discord’s terrible UI other than not using it. The Matrix protocol and Element client are pretty nice alternatives.