Hi Dennis,
It seems to me that the remaining issues are features/bugs related to
the desktop and window manager you are using. So, I'm hoping somebody
else who is familiar with those environments can help you. Until then,
here are a few general remarks.
"Ubuntu Mate" sounds like a bad combination. I have no specific
experience with it but as I recall Ubuntu decided to remove the
application menus from the application window and show it in the
desktop panel. But that requires the Unity desktop, so if you use Mate
desktop you would loose the application menu, no?
I can resize the window by dragging the window border on any of the
sizes top/bottom/left/right and not just the bottom right corner.
I will try to reduce the required height of the window, however, on my
xfce desktop it is already down at 730 pixels.
You should always be able to completely reset gqrx settings by
starting gqrx with the -r option. That should reset any toolbar
settings you may have done.
Alex