I’ve looked at the manual and it seems your best bet would be to manually turn off all image options until you have achieved the equivalent to game mode, except it is still in regular mode so you can maintain 4:3 aspect ratio control.
Basically, go through all options that the manual says cannot be changed when in game mode, and set them to off.
Very limited input resolution options for that tv, sadly…
Edit: perhaps worth a shot to try the settings Marqs posted for his Panasonic oled. https://videogameperfection.com/forums/topic/tv-compatibility/page/12/#post-15034