Tried this, only three tabs available: Console, Sources and Audit. They do not even work. MacOS Big Sur 11.4 with iOS 14.4.2 iPhone.

Downloaded and installed Safari Technology Preview 125 in my MacOS Big Sur 11.4, but now when I try to inspect my iOS 14.4.2 device, the webpage it is on is greyed out so I cannot! Trying to inspect via normal Safari has only Console, Sources and Audit tabs as described by original post. Does the inspectable page have to be delivered over https?