You have totally ruined the look of my home screens.
Previously, I had the Transparent theme set, but there was a separate setting Personalisation>Home screen>Folder appearance where one could pick Light or Dark for the folder background. I had Light set, and the light-ish grey folder background worked well with my Home screen wallpaper .
With 5.6 my folder backgrounds have gone Dark - which means many of them virtually disappear into the wallpaper, and it looks horrible. Rushing back through the new settings arrangement to Settings>Home Screen?Folder Appearance there is now only the shape setting - the light or dark option has disappeared (though ironically that page is showing the shape options in the Light version I want and previously had, even though it is using the dark version on the actual Home screens).
It makes my Home screens look terrible - so terrible I am changing Launchers forthwith until the option for Light folders is restored, though I will check Microsoft Launcher each beta update to see if it has been so I can use ML again.
And no, I am not changing my wallpaper; and no I do not want to use the whole Light Theme, makes the feed and settings pages much too bright and flat. Transparent Theme with Light folder background appearance was fine. Losing that folder appearance option has single handedly driven me from being able to use the Launcher at all.
But the one other comment I can make before/unless/until you restore that folder option so I will even run the Microsoft Launcher again, I did notice that the change you made to the adaptive icons has made it much WORSE than it was. Previously it made just a few of my icons have horrible background colours - now it makes many more. I think the only thing you can do that would make them usable for me is to provide a background colour option offering at least white and maybe mid grey.
But please PLEASE put the option back to have the light theme folder background with the overall transparent theme as it could be before.