I enjoyed using Web Inspector tool from Safari Developer options to debug active web pages in iPhone or iPad. For instance, WKWebView running on iPhone. With the update of MacOS Big Sur 11.4 it got broke !! The Safari (14.1.1) web inspector only limited to Sources, Console and Audit. Also this issue started floating in SO thread here.
Last week I got rescued by a lesser known application (at lest in my team!) Safari Technology Preview from Apple. Safari Technology Preview app will give you full scale options includes the most recent version of WebKit, the rendering engine that powers Safari. It requires a Mac running macOS Mojave v10.14 or later. I highly recommend this Apple provided in-house Browser for Developer.