The output represents the logits of the 22 different classes. You can apply a softmax on the output to get the class probabilities. Each channel represents a probability map for all pixels belonging to the current class. So for example output[0, 7, :, :] will give you a probability map for class 7. To get the most likely classes, you can apply torch.max on the output.
Does this make it clearer or did I miss some points?