Currently the control over Plasma desktop opacity is incomplete and focus on only some elements like panel and its related items, while notifications, Add Widgets sidebar, status OSDs... are not included. For example, while using Light or Dark Breeze theme, having opaque desktop is impossible for now and the only solution is to enable two extra effects (Background contrast and Blur) to fix this problem. From user perspective, having control only over panel opacity seems to be bad and result in inconsistent looking desktop. It would be great to have an option in Plasma settings under Appearance category where user can control how much opacity to be applied to whole Plasma desktop, while letting the option to have adaptive effect or follow global opacity under panel setting.
*sigh* This is something we typically say should be up to the theme itself, but I guess the adaptive Opacity feature kinda opened the floodgates. What do you think, Niccolò?
This really is meant to be addressed by themes! You can switch to an opaque version of the Breeze theme to achieve what you're asking for. The "opaque" button on panels is really only meant for panels and widgets inside of them.
(In reply to veggero from comment #2) > This really is meant to be addressed by themes! You can switch to an opaque > version of the Breeze theme to achieve what you're asking for. The "opaque" > button on panels is really only meant for panels and widgets inside of them. There is no official Breeze version of what you call "opaque theme", and the users don't trust any third party theme due to lack of trust and of sync updates. If the opacity can be achieved on panel components then it should be achieved also to other parts of Plasma desktop or are you considering panel and its components to be separated from Plasma desktop project. The real problem is that an option was introduced to achieve opacity for only one part while ignoring the other parts of Plasma desktop. So either generalize the option by automatically switching to an opaque version of Breeze, or it will always be considered to be incomplete and buggy for many users.
The scope of that toggle was purely fine-tuning the panels and the widgets inside of it, and it was necessary to implement adaptive transparency, without which I would not have added the toggle. I'm not going to add a setting that does exactly what themes are meant to address. If you do not trust theme-makers (I don't quite see the reason though, they cannot include malign code) you can make one yourself; you can only change the dialog background svg and fallback to Breeze for everything else if you want to maintain sync updates to the other files.