i know this is a shitpots but that's 🇳🇮 Nicaragua or 🇸🇻 El Salvador flag

Uninstall all the flatpak packages that are installed as system wide packages and install them as user packages, that way flatpak will use your /home partition. I had the same problem.

First photo is was from Colombia 2021 riots

Edit: thank you for the fix

Install it, use it, love it

By default I have the same issue using KDE and a dark theme, what I do is set a specific theme inside LibreOffice. Another thing you can look for is setting another GTK theme or color scheme inside Customization on Plasma Settings

Use another theme, look for them in Tools->Preferences