ACR - Denoise Tool Preview Box

Hi, 

I'm working on an MBP 2019, its a few years old, it will likely be updated soon, but it has been handling what I do how I have needed it to. 

I have been using the ACR Denoise Tool occassionally. On this old MBP it used to load a Preview Box to show me how it will update my image. It would then take 4 mins (per image) to update and create a DNG file. 

However, now it no longer does this. It just updates the RAW image with the automatic setting of 50, which takes 4 mins to process. As 50 is always too much I move the slider and then it takes another 4 mins to make the new adjustments. Any future adjustments after this doesn't seem to take the 4 mins, but does seem to slow down the computer. 

But if I'm working with more than 1 image, switching back and forth between the two takes up alot of CPU. 

Whilst I appreciate the convenience of having an adjustment slider. At the moment, I prefer the previous way of doing this, i.e having a preview box and creating a new DNG. 

Is there an option to put it back?