AMD has made progress compared to FSR 3 and ensured the stability of the reconstructed image. But FSR 4 is still inferior to DLSS 4 in the sharpness of moving objects, and DLSS 4.5 wins in the clarity of vegetation, character hair, and halo effect.
Summary from Hardware Unboxed:
Overall, DLSS 4.5 gives the impression that the game is running at a higher resolution. (…) If I had to choose one upscaling, I would choose DLSS 4.5 - it gives a better picture, especially in 4K Performance. NVIDIA is still the leader in upscaling quality.
FSR 4 problems remain: not all games support the technology, sometimes you have to use Optiscaler, and FSR 4 is not available on older video cards.