Not sure if this is an iOS issue or the WebUI itself. However, this is the only web interface that I've come across with this issue.
6.9.0 beta 30
iPhone 8, iOS 14.0.1
In both safari and chrome, the only way to pinch or swipe is to be touching the blank areas outside of the UI content boxes.
Trying to swipe (touch to scroll), or pinch (zoom), while touching the content boxes, results in no change.