This filter removes a channel you don't want in your home page or search results. It will still show up if you search for it by name.

www.youtube.com##ytd-video-renderer:has-text(ChannelNameHere)

www.youtube.com##ytd-compact-video-renderer:has-text(ChannelNameHere)

www.youtube.com##ytd-rich-item-renderer:has-text(ChannelNameHere)

This filter removes videos with "reaction" in the title, but you can change it to filter whatever word you don't want to see.

www.youtube.com###video-title-link:has-text(/reaction/i):upward(8)

www.youtube.com###video-title:has-text(/reaction/i):upward(6)

www.youtube.com###video-title > yt-formatted-string.ytd-video-renderer.style-scope:has-text(/reaction/i)

My favorite. This filter removes a comment that only has the word "First" or "First.", ignoring capitalization.

www.youtube.com###content-text:has-text(/^first$/i):upward(6)

www.youtube.com###content-text:has-text(/^first.$/i):upward(6)