Well, Grav is designed purely for creating content-based web sites. Grav really doesn’t have a full framework and is nothing like Laravel/Symfony even though we do use some Symfony components to make the magic happen.
However, it does have a sophisticated plugin system that allows you to develop pretty much anything you want. So you can build complex things if you want. The admin plugin is a prime example of this, it uses forms, email, and login plugins along with the logic in admin itself to build a fully functional admin for Grav. Also there’s a shopping cart plugin that provides relatively sophisticated functionality. So Grav is quite simple to extend and build complex functionality on top of, there really are no limitations, and you can use pretty much whatever PHP technologies you wish.