This is something annoying but easy to fix.
You're using KDE Plasma, but some times the file-picker dialog box isn't the standard KDE dialog... it's some ugly file-picker. Here's the fix.
Before:
The Fix:
The .bashrc file is place where you can set "Environment Variables".
It's located in your home folder: /home/myusername/.bashrc
- add the line
export GTK_USE_PORTAL=1 to the end of your~/.bashrc file. - Log out then in.
This will work for most applications. The fix, is telling apps to use something called "Portals". Which will make things like GTK based apps default to using your system's file picker instead of the builtin GTK picker.
Some apps, like OnlyOffice, don't support this feature yet.
After:
