Input shape is the dimension of the input data, for example in case you have image data a Keras model needs an input_shape of (height, width, num_channels) , if you are feeding a model with an input of (3, 1) the model will learn dependences of three consecutive elements. larger the window more information the model considers about the temporal dependences of observations in the sequence.
Sometimes you can have dynamic input shapes ex, images with variable height/width.  You can check more details here tf.keras.Input  |  TensorFlow Core v2.5.0 2