SUMMARY Okular doesn't open files via File Menu/CTRL+O on Xubuntu. (Case A) STEPS TO REPRODUCE 1. Launch Okular. 2. Go to File Menu. 3. Click on "Open...". (Case B) STEPS TO REPRODUCE 1. Launch Okular. 2. Press CTRL+O. OBSERVED RESULT [ON BOTH CASES, (A) and (B)] Nothing happens. EXPECTED RESULT [ON BOTH CASES, (A) and (B)] Okular would launch a window to browse files in the computer's drives. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Xubuntu 20.04 ADDITIONAL INFORMATION I have tried the same procedures on Ubuntu 20.04 and evertything works just fine.
Honestly, this seems something that you should tell the Xubuntu people, not us.