SUMMARY
This is probably a duplicate, but just providing more reason for the feature.  There are no good pdf sheet music readers available for Linux.  This is a common complaint amongst musicians.  Okular is a SUPERB alternative according to everyone.  There is only one small drawback to using Okular for this.  Most musicians wanting to use a laptop for sheet music reading (who don't want windows) are using touchscreen devices, or 2 in 1 devices.  (ipads are too small for showing 2-pages at once) The device has to fit on a music stand.  And the problem with touchscreen devices is being able to right click can be problematic or just not possible / supported.  Where this affects Okular is when going into full screen mode and then trying to exit fullscreen mode.  There is no way to exit on a touch screen device because we can't necessarily right-click.  A HUGE favor to musicians in this situation would be a way to exit fullscreen without having to right-click.

Thank you for your consideration.

STEPS TO REPRODUCE
1. Go into fullscreen mode
2. Try to exit without having a right mouse button
3. Try to exit on a touchscreen

OBSERVED RESULT
Can't exit

EXPECTED RESULT
Want to exit

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: kubuntu 20.4.1
(available in About System)
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 6.68.0
Qt Version: 5.12.8

ADDITIONAL INFORMATION