Both list and arrays are a collection type of variables that can store multiple values of the same data type. The main difference between them is if their size is fixed or not. Array has a fixed size, meaning that if you create an array containing 3 elements, you can't add more than 3 or reduce its size. List has a dynamic size, meaning that you can add or remove elements as you need. List also provides some methods that can be invoked to perform operations on the elements, such as sorting, reversing, finding, etc. Array does not have such methods, but it is more optimized for arithmetic computations.
References:
* Differences between a list and an array - UiPath Community Forum
* Array manipulation with UiPath (List, Dictionary, Array) - F-PenIT blog
* List Collection ArrayList - Activities - UiPath Community Forum