Get rid of YouTube Shorts + a couple of lesser-used sections in the navigation sidebar.

YouTube-without-Shorts.user.css

/* ==UserStyle==
@name        YouTube without Shorts
@namespace   github.com/nileane
@version     1.0.0
@description Hide YouTube Shorts
@match       *://www.youtube.com/*
==/UserStyle== */

#contents > ytd-rich-section-renderer:not(:nth-child(1)),
#sections > ytd-guide-section-renderer:nth-child(3),
#sections > ytd-guide-section-renderer:nth-child(4),
#contents > ytd-item-section-renderer:nth-child(5),
#contents > ytd-reel-shelf-renderer {
    display: none !important;
}