When comparing the QtWebEngine devtools/inspector to the one in Chromium, certain features are missing or broken. I'm not sure if those all boil down to the same cause or if they are different things (and some arguably are bugs rather than feature requests), but I'm opening this as an overview to hopefully get the ball rolling.

1. The "device mode" toggle is missing, it can be used in Chromium to view the page on a simulated mobile screen:
2. Using <Ctrl-P> and entering "screenshot" allows to select e.g. "capture area screenshot". Both QtWebEngine and Chromium show a cross-hair allowing to select a part of the page. After that, the screenshot is saved as a simulated download with Chromium, but nothing seems to happen with QtWebEngine. (This one might be a bug rather than feature request?)
3. When clicking a color in the "styles" pane, a color picker opens. With Chromium, it's then possible to hover over the page to select colors from there: but with QtWebEngine, that doesn't work.
4. In the "Sources -> Filesystem" tab, using "Add folder to workspace", nothing happens.