SUMMARY
This is a problem because the only way to exit fullscreen mode after triggering this bug is to close Koko. Users may not know the specific key combos to close or switch window (e.g. alt-f4 or alt-tab) and so they may resort to powering off their PC (maybe a bit of a stretch, but I don't doubt that these types of user exist).

STEPS TO REPRODUCE
1. Open a photo
2. Go into fullscreen mode
3. Click the back button
4. Click on a photo
5. Click "Exit Fullscreen"

OBSERVED RESULT
After 3: there is no button to exit fullscreen mode
After 5: clicking the button does nothing
I have to close re-open Koko to exit fullscreen mode

EXPECTED RESULT
Either (1) don't let us go to the image browser view when in fullscreen mode
or (2) have an "Exit Fullscreen" button in the image browser view

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20230501
KDE Plasma Version: 5.27.4
KDE Frameworks Version: 5.105.0
Qt Version: 5.15.9
Kernel Version: 6.2.12-1-default (64-bit)
Graphics Platform: X11

ADDITIONAL INFORMATION