I've been using flutter for a couple of weeks and I can affirm that this framework is great, it's easy to learn and with a single codebase you can create ios and android apps. As you may know, flutter has a large community of developers and this will make the work with it faster and easier.
In this article, I selected for you 5 cool libraries that you may or may not know, so let's start

carousel_slider 2.0.0

Creating a carousel is a good feature fo your apps, it allows you to make a showcase of different elements inside one activity, and this makes the user experiences better.

If you want to learn how to install it and how to use it, visit this link: Carousel

font_awesome_flutter 8.8.1

font awesome is a large library of icons, using this library you will be able to add a large set of icons to your app and make you UI more beautiful

If you want to learn how to install it and how to use it, visit this link: Font awesome

google_fonts 1.0.0

using custom fonts makes your app original and more attractive, google fonts offers you a large set of font ready to use, by using this library you will be able to add fonts without any problems.

If you want to learn how to install it and how to use it, visit this link: Google Fonts

shimmer 1.1.1

Shimmer effect is that glass-like reflecting effect that you see most of the time when there are some elements who loads, it's a pretty effect that will make the user experience comfortable