Perhaps this is opening a can of worms, but I think it’s probably a good idea to expand the “similar kanji” section to include kanji where the radicals look similar too. If I’m right, the section is populated with characters that share a certain amount of radicals in common. However, we end up with some cases like 線 and 緑, where the bottom-right radical is very similar (especially at most reasonable font sizes for reading). If there was a way to expand the list, either programmatically by throwing in a warning about similar radicals (maybe in a secondary list to avoid confusing the person studying), or through a small suggestion form for review by the WK team, I think it’d be helpful!
I think there is a script that does exactly this: [Userscript] WaniKani Similar Kanji
EDIT: Glancing over that thread that specific script may not be working but there are some alternatives linked in the discussion.
I’ll poke into here, thank you (so far none of the links work anymore though ) I did find this really cool script though: [Userscript] Keisei 形声 Semantic-Phonetic Composition
You can edit the kanji list as you like, and it also includes the kanji from Keisei as a source.
As far as I know the default section in WK shows kanji people sent in, it will take a very long time to fill (if someone still know about sending suggestions in the first place).