Hello,
I am not able to run Okular as a Flatpak, I think after the 25.08.03 update but it may be something else. I am running Linux Mint Cinnamon 22.2
What I have:
~$ flatpak list
Okular org.kde.okular 25.08.3 stable system
KDE Application Platform org.kde.Platform 6.9 system
If I run Okular I get:
~$ flatpak run org.kde.okular
/app/bin/okular-bin: error while loading shared libraries: libPlasmaActivities.so.6: cannot open shared object file: No such file or directory
I have established that KDE platform 6.9 is the one Okular wants. I have run flatpak repair on the whole local repo? Any experience with this? Id did run but I can’t remember when it stopped. Having to use an old…snap 
Ta.