On macOS, if the system preferences option found under System Preferences General -> Show Scrollbars -> "Automatically based on mouse or trackpad" is set, then scroll bars are always visible in a QWebEngineView, but they are not clickable.

Attached is an example that demonstrates the issue.
The example shows a QWebEngineView with 2 visible scroll bars, which are not click-draggable, until you use a mouse wheel or touchpad to scroll a bit, after which the scrollbars can finally be dragged.

Ideally the scrollbars should either not be visible, like Chrome Browser does it, or they should be clickable.