Instead of waiting for the next Kanji review, maybe try learning some grammar.
There are plenty books specifically made for that purpose, and they come with exercises that you can do to make sure the grammar actually sticks.
Wanikani only offers kanji and related vocabulary after all, and Japanese (like all languages) is more than knowing words.
There are free online sources for grammar, but I highly suggest either a book like the Genki series, or using the website Bunpro.
Books like the Genki series, will give you a list of vocabulary, a few new grammar points and practice in every chapter. (I’m using the Minna no Nighongo series because I got them when I studied Japanese in college. It’s similar)
Bumpro is like SRS (as far as I know, I haven’t used it. Others are better suited to explain)
If you’re serious about learning, this is what I suggest.