About the top bar and the dock:
After getting your feedback and testing and researching a little more, a combination of designs should be working well.
First, window mode (not perfect mockup/rendering here but enough to get the idea - strange bright line in between):
In window mode, there is a shadow coming from the top bar down, separating the bar from the dock and to lift the dock a little - like the windows. This way we have a nice separation and the bar is also floating in front of the wallpaper on an alike level like the windows.
Maybe we need a shadow for the dock too, if it feels not right to have the dock on wallpaper level only.
Next, the max-windows mode:
We get rid of the shadow and the top bar gets a dark line to separate from the dock and the max-window. So we should have no problems with the shadow from the bar in some circumstances and apps/programs. I would also suggest (not like here in the mockups) that the transparency should be a little less (compared to window mode), but not get lost completely like it is now. This way we have a modern and clean look, also not that heavy like it is now (depending on the wallpaper of course).
Some may notice, this behavior and look is quite the same as in macOS - with the dock and how the windows are handled this is at least for me a nice and simple way to do it. Also, it looks and (hopefully) feels right.
Awaiting your feedback,