Frameworks like Laravel are there for solving most of the "regular" or "normal" use cases, for this kind of solutions you don't need to dig deep into the code, you can just follow the amazing documentation and get going. As I said this applies for the general or common use case, but, at some point in your career if you're lucky, you are gonna reach the point in which you need to extend change or replace one of the core features for a solution that suits your business case and problem.

Symfony took a different path from v4 on, probably this article will help, it can bring a bit of light.

I've professional experience with Symfony and Laravel and in the end, we always end up changing some of the core features for our own bundles/packages which satisfies our business requirements.

It falls to the fact of how much control you wanna have if you ask me on where to start to really understand the core of Laravel go to illuminate/contracts and start checking the implementations.

BTW I also spend most of my first projects (that I actually charged money for) without understanding much of the things happening under the hood.