I use only WK for kanji and vocabulary words; I’ve tried to pick up other learning apps or systems parallell, like Bunpro or Lingodeer, but none of those have stuck in the same way. For grammar I slammed into Genki (like a lot of people do) and lurk a lot on the forums (since a lot of people take pains to explain things well if you ask).
However! I’ve also been reading up on Tofugu’s explanation series about grammar particles. The fact that they focus really hard on one thing per article is something I appreciate a lot, and whenever a sentence structure you come across seems odd it’s nice to be able to vaguely remember ‘oh yeah, wasn’t there this thing…?’ and put it into practice. Their focus isn’t as expansive as most grammar books,
Otherwise I try to keep some Japanese audio around and try to dive into reading, even when I’m woefully underprepared for it. :V Time spent looking up scattered sundries off now can pay off when you re-encounter those concepts or words later–the pang of recognition comes a lot easier when you’ve already sorted it out once, even if you didn’t get it fully then. Something I have fond memories of was helping a friend play through a Japanese-only video game, looking a bunch of kanji up on the fly, desperately trying to remember grammar and overall being mostly completely unhelpful. And yet! A lot of the kanji that I originally looked up back then have come back in my WK lessons, and have been a lot easier to remember the meaning of as a result. Plus, the practice I got hastily identifying distinctive radicals to look up has come in handy whenever I see a kanji I don’t recognize.
This is all a bit long-winded and probably tangential, but the main thing I’m trying to get at is picking up bits and pieces from here and there can help out a lot. Words with odd readings that I’d heard elsewhere stuck immediately, kanji that would otherwise trip me up were familiar, etc. Just looking at or listening to a bunch of stuff, you’ll get a lot of things you can’t process yet, but all you need is a couple of things to stick. (Sidenote: It is entirely possible this isn’t actually a good study method, and I am just addicted to the thrill of recognition.)