FSR4 would benefit from specialized hardware cores used to accelerate Ai based workload. Looking at AMDs site: https://www.amd.com/en/products/graphics/technologies/fidelityfx/super-resolution.html

(Sorry for screenshot, couldn't copy-paste easily.) REdstone is FSR 4 here. The RX 7000 graphics cards here can only use Upscaling. So I would expect any older generation of (and weaker) hardware like Steam Deck should also only be able to use Upscaling, not the full set of features. And because these graphics cards and older hardware do not have the hardware cores to accelerate Ai based workload, they should require more power and latency. Just my assumption here.

The table shows 3 types of upscaling: Spatioal, Temporal and ML-Based. Spatial is without Ai, and the game does not require any support, it's like a Photoshop effect after the image is created (simply speaking). Temporal is more complex, taking multiple images from the game with builtin support from the game to produce better results. This doesn't necessarily require Ai, but AMD decided to combine Temporal with their FSR 2 and FSR 3 with Ai based logic. Now I do not understand why ML-Based Upscaling is not available to FSR 2 and FSR 3. Maybe this requires special hardware that is only available on the new RX 9000 cards... Ah yes, I was right: https://en.wikipedia.org/wiki/Radeon_RX_9000_series#FSR_4

FidelityFX Super Resolution 4 (FSR 4) is AMD's first machine-learning upscaling solution that is able to leverage the second-generation AI accelerator cores in the RDNA 4 architecture.[14] AMD stated that due to requiring hardware acceleration, FSR 4 was limited to the Radeon RX 9000 series.

That means, the FSR 4 version that could be available on Steam Deck is not the same upscaler used on these cards. So we get a FSR 3 styled upscaler (Temporal) only and I wonder how much better it is, if any, and how much more power it draws. I think its important to make this distinction.