How do you actually learn a huge codebase when you can’t afford to slow down?

I started my first big company internship a month ago (non-FAANG tho), and it's my first time working in a genuinely large, complex system. All my past internships were either small standalone projects or simpler stacks.

I use LLM tools for most of my coding to keep pace and meet expectations, but I'm starting to worry I'm generating tech debt faster than actual working code. I feel tunnel visioned constantly, I'm never sure if my approach is even right, and I can't afford to slow down enough to properly learn the codebase.

How do experienced devs deal with this? Am I just supposed to put in extra hours off the clock to catch up?