SUMMARY
On web-apps utilising a canvas object, e.g. WebGL applications
can make advantage of the Pointer-Lock mechanism.
So it is possible to navigate like in a FPS shooter or thelike in a WebGL app.
Hitting ESC or another key action, the programmer defined before, shall exit
that pointer Lock state ageain. The cursor should get visible again.

Locking works on Falkon.
But releasing it again seems not do be possible/properly working.

STEPS TO REPRODUCE
1. Go to following demo: https://mdn.github.io/dom-examples/pointer-lock/
2. Follow the instruction there, click into the canvas to get your pointer locked.
3. Instructions say: to exit lock, hit ESC key, but this doesn't work.

OBSERVED RESULT
It seems, that the corresponding Javascript calls weren't executed/interpreted
accordingly. The Pointer lock cannot be exited anymore.
Only quitting Falkon resets this state.

I also tested other Web-apps and also self-made ones.
Following piece of Javascript requests Pointer Lock:

canvas.requestPointerLock ||
        canvas.mozRequestPointerLock ||
        canvas.webkitRequestPointerLock;

And following snippet shall release it again:

document.exitPointerLock ||
        document.mozExitPointerLock ||
        document.webkitExitPointerLock;

All mentioned Apps and examples perform properly on Firefox and as well on Chromium.

EXPECTED RESULT
ESC Key or otherwise connected event shall trigger the Release of the Pointer-Lock again.
It works as described on Firefox and as well on Chromium.

SOFTWARE/OS VERSIONS
Windows: --
macOS: --
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.16.4
KDE Frameworks Version: 5.61.0
Qt Version: 5.13.0

ADDITIONAL INFORMATION
URL for testing pointer lock: https://mdn.github.io/dom-examples/pointer-lock