Fix to have a "Borderless Window" experience on KDE without any white borders:

1. Set the game to windowed mode, with your respective montior resolution
2. Open System Settings, then go to Window management>Window Rules
3. Create a new rule, set it above all others, if any
4. Confiugure the rule like so:
   1. Description: Anything you desire, this will be the name on the list.
   2. Window class: Set to Substring match, then on the field type steam_app_553850 steam_app_553850
   3. Match whole window class: Yes
   4. Window types: All
   5. Window title: Substring Match, type HELLDIVERS™ 2
   6. Click Add Property, Poistion. Set to "Force". This depends on your resolution and multi-screen setup if any. If you only have a single monitor, 0x0 would work fine. If not, use "Detect Window Properties" with a fullscreen window (can be any window) on the screen you want the game to be.
   7. Click Add Property, Size. Set to your resolution (Actual monitor resolution, not the resolution you told the game to be rendered at.)
   8. Click Add Property, Ignore requested geometry, Force. Select "Yes".
   9. Click Add Property, Keep above other windows, Force. Select "Yes".
   10. Click Add Property, No titlebar and frame, Force. Select "Yes". Click Apply, and reboot the game. It should work flawlesly, you can minimise and maximise the window freely.