I’d give it a while, the common wisdom here seems to be that starting grammar at around level 10 is a good idea, since you’ll probably know most of the really basic kanji you’ll encounter in beginner grammar practice. If you want to start earlier than level 10 (not a bad idea), I’d recommend LingoDeer, it’s kinda like Duolingo but more focused on Asian languages, while afaik Duolingo can be a pretty bad way to learn grammar because of how it’s structured
and LingoDeer doesn’t have a psychotic murderer for a mascot.
It’s important to keep in mind that WK will start to pick up for you if it hasn’t already. That’s another reason why you may want to wait to really start grammar, so you don’t get blindsided by the massive uptick in reviews and lessons. By level 10 you’ll probably have a pretty solid routine down that will let you fit in time for grammar too.
If you don’t want to pay for Lingodeer (Pretty sure it’s only $20 for a lifetime membership), there’s plenty of great free grammar resources that you can find all over the forums.
As far as feeling like you aren’t making any practical progress, trust me when I say I totally get it. I’m a good way into WK (far enough at least that I’m not quitting at this point) and I still know next to nothing with grammar, because I’ve been focusing on WK too much and Lingodeer not enough. No matter what you decide for grammar, remember that languages are complicated and you may not feel like you make any “real” progress for a while, but just keep showing up and you’ll get there. The most important thing is to stay consistent with your studying. 10-15 minutes every day is so much better than an hour of cramming once a week, and you’ll eventually start to see results, trust me.