[MU4 Issue] Context menus have thick black outline on WMs with disabled translucency

Describe the bug
Context menus have a thick black outline. I strongly believe this is due to missing support for window managers without translucency, because I saw similar bugs in some (not all!) other Qt programs.

I personally use xfwm4 on X11, with translucency disabled. I guess that this happens on some other window managers, too.

However, MuseScore's code looks like it tries to detect and handle that: https://github.com/musescore/MuseScore/blob/326d4706593f234e3ec391a67cb5598871e1b4c8/thirdparty/KDDockWidgets/src/private/Utils_p.h#L146-L153 (found via a quick search; the lines around it look right, but I didn't look at it in detail.)

To Reproduce
Steps to reproduce the behavior:

1. Use xfwm. (Probably the easiest way to do it is to run a Virtual Machine using VirtualBox/qemu/whatever, install Debian using an image like this, and select "xfce" during the installation process.)
2. Disable compositing (run xfwm4-tweaks-settings, in the tab "Compositor" uncheck the box "Enable display compositing")
3. Open MuseScore (e.g. by downloading it as AppImage)
4. Right-Click somewhere

Expected behavior
A nice context menu appears.

Actual behavior
A context menu appears, with very thick, black outline, that doesn't look like it's supposed to be like that.

Screenshots

Here's what it looks like:

Here's what it could look like (not a Screenshot, but rather edited to look less terrible):

Here's how to configure xfwm4, in case you want to reproduce step 2 exactly:

Just in case someone thinks my setup is broken and no Qt app can possibly work on my system, here's frescobaldi, which has a Qt UI, showing a context menu:

Platform information

• Linux, specifically Debian
• X11, with xfwm4 as window manager, and translucency disabled (see "To Reproduce, Step 2")

Additional context
The code looks like setting KDDW_NO_TRANSLUCENCY might have an influence, but it doesn't change anything. Running it as KDDW_NO_TRANSLUCENCY=1 ./MuseScore-4.0.0-x86_64.AppImage shows the same black thick border. Either I'm doing something wrong (very likely), or perhaps AppImage prevents the envvar from reaching the windowManagerHasTranslucency function. Or I simply misunderstand something, and MuseScore can't handle non-translucent window managers at all.

Also, whenever a context menu is opened, the following line appears in the log:

22:15:12.816 | WARN  | main_thread | Qt         | QQmlComponent: Created graphical object was not placed in the graphics scene.

I'm not sure whether this is related.