SUMMARY
Presentation mode seems to be broken in the RC 2 with Qt 6.7 and any scaling different to 100%. Perhaps not specific to Okular and related to this other issue also affecting VLC's fullscreen mode: https://bugs.kde.org/show_bug.cgi?id=481456

However, with Okular the fullscreen mode works just fine.

STEPS TO REPRODUCE
1. Open a PDF
2. Click View -> Presentation (or Ctrl + Shift + P)

OBSERVED RESULT
Content is not shown correctly. See recording here:
https://drive.switch.ch/index.php/s/erLT2ooQ6wPjXsY

EXPECTED RESULT
Presentation mode should work as in previous versions.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.93.0
KDE Frameworks Version: 5.249.0
Qt Version: 6.7.0
Kernel Version: 6.7.5-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 8 × 11th Gen Intel® Core™ i5-1135G7 @ 2.40GHz
Memory: 15.3 GiB of RAM
Graphics Processor: Mesa Intel® Xe Graphics
Manufacturer: LENOVO
Product Name: 20XYCTO1WW
System Version: ThinkPad X1 Yoga Gen 6