Ubuntu is a popular OS for raspberry pi that has a apple OS look, and a easy to use desktop with a software store built by Ubuntu. Ubuntu has a lot of features that you will not find on Raspberry pi OS, such as better graphics, additional drivers, and apps such as unity and unreal engine that have been specifically made for it. It is also free and open sourced so anyone who wants it can use it.

If you are wondering what OS to choose then get both. Just have two separate SD cards and test them both out to see which one that you like. When using it make sure to have a large SD card because it will take up a bit of space. There are multiple versions. Depending on what Raspberry pi that you have get the correct version. If you are looking for more of a coding experience on your raspberry pi, choose pi OS. If you are looking for more of a desktop experience with more apps and games, choose Ubuntu. You can download Ubuntu here. You can also download and flash it straight from the pi imager, inside of the general purpose section.