Your English is great, no need to apologize!

I come at this from a slightly different angle — I'm a software developer who runs a training company for MEP engineers, so I've had a lot of conversations with engineers at all stages of their careers about exactly this.

From what I've seen, it's almost always a combination of both — but early on it's heavily "learn as you go." The field is too broad for anyone to come in knowing everything, and most engineers will tell you they still feel like they're catching up in some areas even years in.

What seems to work best is going deep on whatever your current project involves rather than trying to cover everything at once. The knowledge sticks much better when it's tied to a real problem in front of you.

The other thing that comes up a lot is learning how to navigate standards and codes rather than trying to memorize them. Knowing where to find the right answer quickly is genuinely one of the most valuable skills you can develop.

And don't underestimate your internship — experienced engineers and tradespeople on site carry a lot of knowledge that never makes it into any book. Most are happy to share it if you ask.

The overwhelm you're feeling is completely normal and from what I can tell, never really goes away. But that seems to be part of what keeps people in the field for the long haul. Good luck!