Stablecascade super-resolution controlnet is already available.

This workflow is the simplest example. However, due to the size of the stageB , it may cause errors. Please change the image or modify the size to stardard SDXL size (such as 1024*1024)  before testing.

Some photos may result in blurry results.

Super-resolution controlnet is available at huggingface. (for using the controlnet ,update your comfyui first)