Frame generation will make your game feel more fluid at (minor) expense to input lag by generating "in between" frames. It works like Nvidia's DLSS 3 but on any graphics card because AMD open sources it
It will make it look more fluid. It will feel like it's running at a lower framerate, and at the framerates BG3 runs at on the Deck, around 25fps or 40ms per frame, the increase would be quite noticeable.