Unsuccessful: Adding "-console" to the Steam launch options of the game.
Tilde, with or without Shift etc., doesn't call the console. And none of the below attempts affected the FieldOfView. :(
Unsuccessful: Adding these to section "[Engine.PlayerInput]" in the file "C:\Users\[username]\Documents\My Games\Styx\StyxGame\Config\StyxInput.ini
Bindings=(Name="F1",Command="FOV 140",Control=False,Shift=False,Alt=False)
Bindings=(Name="F2",Command="FOV 140",Control=False,Shift=False,Alt=False)
Bindings=(Name="F3",Command="FOV 130",Control=False,Shift=False,Alt=False)
Bindings=(Name="F4",Command="FOV 130",Control=False,Shift=False,Alt=False)
Bindings=(Name="F6",Command="FOV 120",Control=False,Shift=False,Alt=False)
Bindings=(Name="F7",Command="FOV 120",Control=False,Shift=False,Alt=False)
Bindings=(Name="F8",Command="FOV 110",Control=False,Shift=False,Alt=False)
Bindings=(Name="F10",Command="FOV 110",Control=False,Shift=False,Alt=False)
Bindings=(Name="F11",Command="FOV 150",Control=False,Shift=False,Alt=False)
Bindings=(Name="J",Command="FOV 120",Control=False,Shift=False,Alt=False)
Bindings=(Name="K",Command="FOV 120",Control=False,Shift=False,Alt=False)
Bindings=(Name="L",Command="FOV 120",Control=False,Shift=False,Alt=False)
Absolutely no effect. Same for this (and other key examples, see above) in StyxOptions.ini
KeyboardBindings=(Name="F11",Command="FOV 120",bFixed=True)
Absolutely no effect. Same for changing this setting in StyxSystemSettings.ini
CSMMinimumFOV=40.000000
and for changing this setting in StyxEngine.ini
FOVAngle=90.000000