Honestly at this point, I feel like you need to take a break from your projects just... Mentally. Even if you know where the plot is going, or where you want to take it, not knowing how to get from B to G can be a headache. Or even, B to D. What is that magical "step number C" in between?
Summary
I've quit projects cold turkey accidentally, and even with the intention to continue writing with them, only for it to just... never happen. I cannot relate with the comic aspect - of drawing and not having motivation or any of that stuff, personally. But burnt out and story problems, certainly can. I've been working on my project for a decade, and it's certainly no secret to anyone that I'm always surprised by how long it is, by how much it seems like is to still tell, and that it just... keeps remaining in long-form.
For me, personally, it's been comforting to have a realization that my storytelling is not episodic (ie an episode of Phineas and Ferb), where you can drop into any episode, in any season, and understand what's going on with no other context. My writing style is instead, very chronological - if you jump in at chapter 35, you'll probably be confused, and even worse off if you start at 75. I didn't really grasp that in the past - in that, I used to abhor the creator Ranma 1/2 and Inuyasha for never resolving things. Only to realize that while the majority of the series are episodic, they also work very fine as a chronological story, that just happens to be super long.
This past year in 2021, I've done almost no writing. I've been instead working on art work and other business things. I've let my mind wander into lore theorizing with Genshin Impact, and other video games. And while I still keep thinking about my main project and main story, and beat myself up daily about not working on it, I know that I am working on it. Subconsciously.
Really, the best I can say, is to treat a long project like a relationship. You'll argue with it, change and grow with it, and need to have communication with it. This past year I've been, besides not writing, watching a lot of a youtube channel called "Cinema Therapy", and it's oddly given me ideas and insight about healthy relationships - with my writing. It's okay for it to be my obsession and that thing I always come back to, but it's also okay for it not to keep me up until 6am after having written in a grumbling mood for 8 hours. I'm probably not wording this right, but what I mean is that just because you're "not actively producing a new chapter - a new thing - a new art!" every three, or five days, or every week, doesn't mean "you're not working on it". Your brain is working on it. Letting yourself "get distracted" by other things that are fun in the moment, for me at least, are a good thing. Because if I don't "let myself do that thing", then I can't actually focus on the big project. That "thing" will be demanding my attention.
(( I wanna watch Encanto. Never seen it. Sounds good. Can't focus on writing, let alone even open the document, or write little details. Until I carve out time in the dead of night when I should be sleeping, and go F it, and just rent the movie on amazon and watch it. After I did that, watched whatever it was (this case it really was Encanto), my mind was able to focus on writing. ))