Ask HN: Can you learn too much at once?

I'm not the brightest nor fastest learner. I’m 28, have 6 YoE, and TC is peanuts. I went to a small state school in CA and work for a noname company. Nowhere near FAANG, tier2 or tier3 companies. I have been studying grokking coding interview in depth working with arrays, two pointers, sliding windows at the moment. It seems like I'm forgetting how I even solved the problems. I'll solve a medium problem on my own without help or hints. But a few days later I’ll go no leetcode I've completely forgotten how I even solved it. I’m not memorizing code; I’m going thru the problems on my scratchpad and solving them, then coding up a solution. I’m also slowly reading Designing Data Intensive Applications and system design.

On top of this, I learn languages as a hobby, currently working on Japanese and Cantonese. I have tutoring sessions once a week along with a class. I attend these activities, but feel my progress of learning the languages is also quite slow. I’m visiting a therapist for 6 months now(self worth, childhood/drug abuse.. not the point of my post), a month sober from marijuana addiction

I’m wondering if it’s possible to be trying to learn too many things at once or am I just a slow learner whose maxed out his potential? Can the human brain consume all this info at once? Can the brain multitask to the point where information and progress/knowledge is not really retained?