Metacity | The standard window manager for GNOME

The simple answer to your initial question is Yes.

From your question, I am not sure of all the combinations you have tried and what doesn't work for each. It isn't clear if any of the QtWindowsFlags other than Qt::WindowStaysOnTopHint are working for you.

The following Qt5 widgets windowflags example provides something you can use to test the behavior of the various WindowFlags.

Between using Window Flags, WindowRole, you should be able to set _NET_WM_ALLOWED_ACTIONS and _NET_WM_WINDOW_TYPE using Qt5 via XCB and Metacity should respect it as per their compliance file.

From examining the source code as long as recalc_window_features is called, then both the title bar if any and the right click menu shouldn't have close or minimize.The relevant source code for this located at here and here on the Qt5 side, and here on the Metacity side, in case you need to patch, trace or debug further.

As suggested by Scheff, one way of solving your problem is setting FramelessWindowHint, however I believe based on my inspection of the code that you will have more luck setting window flags in order to trigger the special case located here.

E.g.

Solved. It was due to some misconfiguration in my user environment. I have create another user on my laptop and now the google sign in works.

Your shell script has xsetroot -solod grey when it should be xsetroot -solid grey. (I would have added this as a comment but I'm below the 50 rep threshold.

Your vnc log file tells you about problem. You need to install few packages:
sudo apt-get install metacity gnome-panel

UPDATE 1:

You need only x-window-manager or metacity. Both provides window manager and you need only one. From screenshot I see only two problems - grey screen and missing indicators.

To fix missing indicators install one more package:
sudo apt-get install indicator-applet-complete

To fix grey screen you need --force-desktop commandline option. And if you don't want default nautilus window you can add --no-default-window:
nautilus --force-desktop & or nautilus --force-desktop --no-default-window

Also GNOME Flashback (Metacity) session in Ubuntu 16.10 use unity-settings-daemon not gnome-settings-daemon. Don't forget to install it if you decide to change that.

To get better working desktop you also need to exports:

You're trying to do your logic in the wrong place. You need to handle it in the substitution pattern, not in the regex pattern itself.

First, let's write a pattern which will identify the different parts of your string:

You have indeed written this correctly: and the appended \n is the idiomatic way of not delaying the beep output.

But alas modern operating systems allow users to configure their environment so such beeps are suppressible. That's probably what's happening here: looking a little deeper into your question it seems that your shell has disabled beeping on standard output.

Finally, after some research, it turns out that most Window Managers, at least those that do reparenting, stacking and/or compositing sends a ConfigureNotify event to their clients with synthetic bit flag sets to true (e.g. with MSB set on XCB's response_type), whose x and y set to the client window's absolute position. Confirmed with Xfwm4, Openbox, metacity and KWin.