Is it possible to make high quality graphics entirely in Unity?

I’m new to Unity, and I want to make a game from scratch, not using any microgames. In my game, I want good, high-quality graphics. However, is it possible to make believable graphics in Unity? Because when I try to search online, all I get are packages from the Asset Store. I don’t like to use the Asset Store for two reasons. One, most of the packages cost money. Two, I want to make a game entirely from me, and not using anyone else’s work.
I also read online that you could make high-quality graphics by using an external application. However, that isn’t what I’m looking for; I’m looking for graphics entirely made from Unity.
So I’m asking if it is possible to make great graphics by Unity?
Thanks in advance (and sorry if I sound a little stubborn).

Note: I use Unity 2019.4.17f1 LTS Edition of Unity Engine.

To clarify something:

While you &#42CAN&#42 create 3D models and audio in Unity, it is not the ideal utility to do so by any stretch of the imagination. The tools to be able to do so would be made by a 3rd-party, such as from the Asset Store (if not self-made).

As far as modeling goes, Blender is the most typical, high-capability 3D modeling program at no cost to you.

While it's rather tedious to learn to use separate utilities to generate various elements that all go into a single game, it's still worth understanding (and it's made much more clear as you use the other tools) that each different program will generally be good at what it does; audio editing software, modeling software, image-editing software, programming/script-editing software, and more can be used to create the assets that will come together in Unity to create a game using them together.

Of those, only the script-editing software is provided essentially as directly as possible (as an example: Visual Studio), since it needs to be/can be directly linked to the Unity editor for the most fundamental element(s) of making the game(s), the programming code.

No you cant make hi fidelity graphics just in Unity or any other game engine for that matter (read most: Blender technically can have a game engine bolted onto it). To do that you are going to need graphics tools for creating textures, 3D modelling and sculpting tools etc.

You cant and IMHO shouldn’t be trying to do any of this in Unity unless its procedural generation or augmentation of those assets.

Try fireworks or dreamed very for graphics