This is an excellent series of videos developed by Grant Sanderson.
But what is a neural network?
https://www.youtube.com/watch?v=aircAruvnKk
Gradient descent, how neural networks learn
https://www.youtube.com/watch?v=IHZwWFHWa-w
What is backpropagation really doing?
https://www.youtube.com/watch?v=Ilg3gGewQ5U
Backpropagation calculus
https://www.youtube.com/watch?v=tIeHLnjs5U8
But what is a GPT? Visual intro to transformers
https://www.youtube.com/watch?v=wjZofJX0v4M