I just noticed behavior when testing #107765.

Steps to reproduce

1. Copy the sample from https://master-api.flutter.dev/flutter/material/Scrollbar-class.html.
2. Choose either of the Scrollbar and add a custom thickness: 20.0.

One of the solutions suggested in #102775 (comment) is to add the following lines

ScrollConfiguration(
          behavior: ScrollConfiguration.of(context).copyWith(scrollbars: false),
          child: ListView.builder(
              ...
              ...

I'm not entirely sure this is the exact solution to this issue. IMO, it should show a single scrollbar when I wrap ListView with the Scrollbar widget.

If using ScrollConfiguration to scrollbars: false is the correct way, this should be documented in https://master-api.flutter.dev/flutter/material/Scrollbar-class.html with an example.

cc: @Piinks