I noticed that some radicals we study here don’t appear on other lists, and some of them are considered kanji, not radicals. Some of them, also, have other meanings. Why are these big differences between radical lists?
Most WaniKani radicals are not official radicals. They’re kanji building blocks that were given memorable names by Koichi in order to better memorize kanji. Some will match official radical lists, but it’s a very rare occurrence.
WK uses the term “radical” for “kanji parts”. It doesn’t have the same definition of “radical” as understood by other linguists.
WaniKani gives fairly arbitrary names to radicals. They may have other names in a dictionary, but that doesn’t matter because the radicals are chosen to make good mnemonics and you won’t need the names anywhere outside of WaniKani
See the following for list of official radicals, if you’re interested https://en.wikipedia.org/wiki/List_of_kanji_radicals_by_stroke_count
The official radicals can be useful if you’re using a Japanese kanji dictionary, but with Google I don’t think it’s too important anymore unless you’re in a setting where you have to teach/explain kanji to someone formally. If you do want to learn the real radicals, @Kumirei’s list is a good one.