We see you have ZorinOS Pro (gnome DE), but we don't know your hardware or settings.
Can we assume you did the basic checks before creating your ZorinOS installer USB and installing ZorinOS as described here: Before you install
Can you post some details of your hardware, particularly graphics card/s, monitors etc.
Also, are you using fractional scaling?
Is Firefox the one that is packaged by Zorin i.e. an apt, or do you have Snap or Flatpak version.
Is your VLC an apt or Snap or Flatpak?