I know this is an older thread but it got me on the right track so I thought I’d post my solution. I used necival’s solution as a base starting point. I found that zooming in worked really well with it but zooming out didn’t work so well. So I decided to basically normalize the pinch axis value between -1 and 1. However, this is tricky because anything greater than 1 is considered zooming in. So, I had to do two separate normalizations but the Zoom calculations could stay the same.
The above picture where the pop is blocking the node is a subtraction node