Apex Legends constantly starts in Windowed mode, despite setting the option to Fullscreen?

Here's what worked for me:

1. Click Apex in My Game Library (Origin Launcher)
2. Click the Settings icon next to the Play button
3. Choose Game Properties
4. Choose Advanced Launch Options
5. Under Command line arguments, enter -fullscreen into the text box.
6. Save and start the game.

Reference

Okay, so here's the method I found that works:

1. Go to %USER%\Saved Games\Respawn\Apex\local\ and locate the videoconfig.txt file
2. Open it in a text editor and set the value setting.fullscreen to 1
3. Save the change and close the file.
4. In the file explorer, right click videoconfig.txt then select "Properties"
5. Make sure the attribute "Read-only" is checked.

Hopefully Respawn pushes out a fix that addresses this in case I need to change graphics options later.

Ready for the simple version?

UNLESS YOU'VE CHANGED SOMETHING, if you switch focus while Apex Legends is starting up, it will start windowed. If you start Apex and leave your computer alone, it will start fullscreen.