Hi Murat,
From MATLAB R2022a "nntool" has been removed. Instead "nnstart" provides graphical interfaces that allow you to design and deploy fitting, pattern recognition, clustering, and time-series neural networks.
But as per MATLAB R2025a, I cannot find any direct way to create more than 1 hidden layer. But you can create a custom neural network using "network", it creates custom shallow neural network.
For more details refer to the below dcoumentation link:
