Hey @5uper_5ensitive,
In order to play Apex Legends in Steam it would need to be connected with an EA Account. If you were to unlink the Steam account from your EA Account, the next time you try playing Apex Legends it's going to ask you to connect it with an EA Account.
As far as your game progress, you shouldn't actually lose anything by unlinking a Steam account. Since your progress on Steam is the same progress as what you would have in Origin, it should still be there on your account.