Hi there. You have a genuine forum thread (these are becoming less and less common nowadays) and so I'll try to offer a genuine response.
18 months (year and a half) and you are already this high rated? Wow. That's no small accomplishment for sure. Everyone progresses differently, but it took me one year of hard work to cross 1500 rating on here (rapid) and then I got stuck around 1600 for many months and that was a real struggle. You seem roughly this rating (slightly higher) when you are beginning to plateau. Lots of things helped me push past this rating range, but for me it was mostly increasing my positional chess knowledge and this started with beginning to understand and exploit holes and outposts and things like this. You also mentioned having "0 knowledge of strategy and strategic play" so perhaps what worked for me might also work for you too. There is something bigger at play here though...
You play 10+ hours straight? Your post is beginning to sound a lot like me back then. I used to play long chess sessions like this too. I mostly played 10 min chess with no increment and I would sometimes play for like 8-12 hour sessions too, but what I realized was that in a "normal" 8 hour session, it would go something like me gaining 20 rating points after 3 hours, then dropping like 50 rating points and then climbing back up about 30 rating points over the next several hours; my rating would barely move at all, but my best chess would usually happen in the first few hours, so what did I do? I shortened my sessions. 10+ hours is crazy stamina and sometimes I still play much longer sessions, but usually I just play for a few hours (like 3 or less). You may also need to check out my stop-loss system video; it's a bit of an older one for my channel, but still worth checking out.
After this video, I would also work on the things you believe you need to work on (assuming you want to keep working on your chess). You said, "I'm trying to study openings, but it does seem to be broad, and I lack endgame tactics, most importantly, I have 0 knowledge of strategy and strategic play." You probably know your game best. Pick one of those things and work on that.
However, it is also important to decide if you want to keep working on chess at all, or more specifically how much effort you want to keep investing into chess. For this, I recommend this blog post of mine you may find helpful: https://www.chess.com/blog/KeSetoKaiba/chess-motivation-through-purpose
Here is the stop-loss system video:
I'm well aware of how everyone faces challenges while playing chess, and has a point where they get stuck which may lead to quitting. I've played chess for approximately 18 months. My rating deviation shows that in some specific moment, my rating increases for a very short amount of time. When I play during that specific period, I feel like I can focus, and the quality of the game is generally high as well. I play 10+hrs straight which leads to a rating increment. Yet in most cases, I fail to focus and my rating gradually decreases. (the more desperate I become, I tend to drop more ratings & lose focus => bad quality game & burnout period) I've overcome with most burnout-period but now I feel like I couldn't get past this novice level. I'm trying to study openings, but it does seem to be broad, and I lack endgame tactics, most importantly, I have 0 knowledge of strategy and strategic play. I'm overwhelmed by the amount of problems I have in chess, and I don't want to admit it, but I am losing interest. I do want to enjoy chess and be skillful at the same time. I need advice to overcome the overwhelming feeling itself and chess-related advice.