There’s 112 waking hours in a week, give or take, if you’re getting reasonable sleep at all. So, working 70-90 hours per week leaves literally no time for anything else. If you commute and eat and so much as watch a tiny amount of YouTube or Netflix, that uses all the remaining time. It’s very important to realize that working 80 hours per week is trading your
entire life for your salary. Not just some of your time, but all of it. It’s not possible to do any self growth or change things when working that many hours, so turning it around requires working fewer hours.
I’ve done stretches of 80 or even 90 hrs/week for months, and can verify that does induce brain fog and self doubt and a lot of things you’re describing. I have a strange and maybe contradictory take on this - I don’t regret it but feel like I shouldn’t have done it, and I wouldn’t do it again, if that makes sense. I take responsibility for choosing to work that hard because I’m sometimes perfectionist and sometimes people pleaser. Maybe you are too. In my case, there were usually other people around me also working hard, and I eventually saw some financial benefit, and I did get a good reputation. If you don’t have any upsides like that, it’s time to shake it up and defend yourself and your time. At some point I realized that salary is not linear, that overtime can’t pay enough to make 80 hours/week worth it for me. Also I saw more benefits by changing jobs.
Solving code problems from scratch and learning data structures and algorithms and writing libraries are things that generally happen as a byproduct of other goals, people almost never do these things purely for the sake of coding. If one of your goals is to go deeper into code, consider doing a graduate degree perhaps. You can get paid to learn and think about algorithms. LeetCode is not designed to help people be better at algorithms nor coding from scratch, nor is it designed for educating people how to architect solutions. Do not measure yourself by LeetCode.
Last but not least, it takes time and effort to be social, and can even be scary or painful, but it’s maybe worth leaning into that discomfort a little and making it a goal to develop some social muscles. It may take going out on a limb and inviting other people to do things, and when others are scared or busy it might feel like rejection. But this is how networking happens, people spending time with each other. One of the potential benefits of going back to school is a certain amount of built-in social environment, but if more school isn’t your thing, try meetups or a job in a bigger company.