There are quite a few things that do just that. Just search for visually similar kanji on the forums.
There’s a userscript called Niai which expands on the visually similar kanji section that WaniKani already has: [Userscript] Niai 似合い Visually Similar Kanji, this website for looking up similar kanji, homonyms, and synonyms: Introducing Niai: Lookup similar Kanjis, Homonyms, Synonyms and this extension of the self-study script that let’s you study visually similar kanji: [Userscript] Open Framework: Visually Similar Kanji Filter.
There’s also the [Userscript] ConfusionGuesser which guesses which other item you might have confused a vocab or kanji for during reviews.
Also, if you really want to do this you can go to https://jisho.org/#radical (or another dictionary, lots of them have radical search) and choose the specific radicals you want to look for.
And see @ekg’s answer below for some better suggestions!