In a neural network, is it possible to gradient descent with more than one input?
As to what I understand from your question, yes you can have multiple features (variables/input) and use gradient descent to minimize the loss function which has the input variables. Here is an article that gives you a basic vector calculus idea as to what exactly does a gradient is and what it does in the algorithm!
https://towardsdatascience.com/wondering-why-do-you-subtract-gradient-in-a-gradient-descent-algorithm-9b5aabdf8150