Bug 443482

SUMMARY
Using KDE (Plasma,X11) in a VirtualBox, I was not able to switch the full-screen mode using the standard AltGr+f shortcut of VirtualBox. 

Background: Virtualbox uses AltGr+f as the default HOST shortcut. HOST+f is the standard shortcut to switch the screen mode (e.g. scaled to fullscreen) while using e.g. KDE Neon in VirtualBox. 

I am not a developer, I am not sure if "krunner" is the correct package for this report. 
 
This might be related to bug #295633 and #356773

STEPS TO REPRODUCE
1. Start KDE Neon in VirtualBox. Switch the view to "scaled view" via the GUI of VirtualBox.
2. Enter AltGr+F to switch to fullscreen mode
3. krunner opens showing the special glyph (if the cursor is over the desktop)

OBSERVED RESULT
The shortcut is not recognized by VirtualBox - instead, KDE handles the shortcut as the input of an alternative glyph/letter. 

EXPECTED RESULT
Switch the screen mode to fullscreen. :-) 

MY LITTLE ODYSSEY:
- First I thought that AltGr+F is a shortcut to open krunner. (This is a trap!) 
- Then I tried to disable krunner
- Then I realised that krunner opens only if I have my cursor above the desktop
- Then I tried to disable the opening of krunner when the cursor is  
- What makes this issue really ugly, is that there is no easy way in Virtualbox to go back to fullscreen without the shortcut - once you are in scaled model. 

I am not a computer expert! It seems that AltGr+f is always interpreted as typing a letter in the KDE/Plasma Environment. Virtualbox could "not seee" the shortcut. 

WORKARROUND:
Change from default HOST key (i.e. AltGr) to a different key (e.g. Win+Alt) using File>Preference>Input>VirtualMachine>HostKeyKombination in VirtualBox.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE Neo (in Virtualbox) running on LinuxMint

I hope this might be useful. I just spend half an hour understanding whats's going on. :-)