You can hide all of that on your sidebar customization settings, but yeah it’s annoying that it’s turned on by default. The Discover is occasionally useful, but I honestly use Overseerr for discoverability more than I use Plex’s built-in search.
My biggest complaint with Plex is the lack of support for .m3u8 playlists. I want to be able to give it a list of livestreams, and then tune into those via Plex. Plex obviously already has live-streaming support built in via their Plex channels, but they have actively worked against custom livestream playlists, (it used to be supported via an extension, but they removed extension support.)