error Linking to your EA Account requires the steam overlay to be enabled.

Heya, 

In your current case, Apex wants to open a pop-up where you can log into your EA Account, which can be necessary in some cases.
But since you have the Steam Overlay disabled, it's not able to open this pop-up.

Follow these steps to turn on your Steam Overlay:

1. Right Click Apex Legends in your Library
2. Click on "Properties..."
3. Turn the "Enable the Steam Overlay while in-game" setting on
   
   

If it's still not working, then it's possible you might've disabled the Steam Overlay globally for all your Steam games.
To enable to overlay globally:

1. Navigate to the top left of your Steam window and click on "Steam"
2. Click on "Settings"
3. Navigate to the "In Game" section of the settings
4. Turn the "Enable the Steam Overlay while in-game" setting on

Once you've done that, restart your game/steam, and it should work as intended.