You set FSR on, and then a level of it usually called something like Balanced, Performance, Quality, etc. Sometimes its a % slider of a render scale. Then the game is like you were experiencing with your previous set up, rendering internally at a lower resolution, and then within the production of that frame it is being upscaled to 1080p and sharpened. You set in game resolution to your display resolution, and then the quality setting for FSR determines what the render resolution is. Sometimes there will also be a setting for sharpening.
I wouldn't use any other upscaling if you're already using in game FSR. The in game version is also the best to use as it's better implemented within the game to cause less issues with things like HUD elements.
You set FSR on, and then a level of it usually called something like Balanced, Performance, Quality, etc. Sometimes its a % slider of a render scale. Then the game is like you were experiencing with your previous set up, rendering internally at a lower resolution, and then within the production of that frame it is being upscaled to 1080p and sharpened. You set in game resolution to your display resolution, and then the quality setting for FSR determines what the render resolution is. Sometimes there will also be a setting for sharpening.
I wouldn't use any other upscaling if you're already using in game FSR. The in game version is also the best to use as it's better implemented within the game to cause less issues with things like HUD elements.