There was no regression between 25.0.2 and 26.0.0. In your example, the colors look distinct enough to me. Do you have HDR enabled on your display? Maybe a subtle difference in contrast settings is the difference? In either case, you can work around this by setting the scrollbar colors in the apptheme_profiles in <config>/user.cfg.xml. Try adding this before </options> near the end of the file.
This change makes the scrollbar handle lighter: (and window background colors too)
<apptheme_profiles n="apptheme_profiles.Dark" version="1">
<window v="0x303030"/>
</apptheme_profiles>
This change makes the scrollbar background lighter (and effects a lot of other things too):
<apptheme_profiles n="apptheme_profiles.Dark" version="1">
<button v="0x504040"/>
</apptheme_profiles>