tf.keras.layers.SimpleRNN takes input of shape 3D tensor, with shape [batch, timesteps, feature].  For more information read tf.keras.layers.SimpleRNN  |  TensorFlow Core v2.7.0.
If you want feed matrix as input, you can simply flatten the input
example,  Assuming that your (3,4) is a matrix,
input = tf.keras.layers.Input((3,4)) #none,3,4
x = tf.keras.layers.Flatten()(input)  #none,12