Doesn't MetalFX Performance switch to using a spatial upscaler instead of temporal?
Do you see the same performance if you run at the pre upscaled resolution manually? Usually with DLSS/FSR your upscaled framerate should be pretty close to the framerate of the pre upscaled resolution (if you manaully switched to that resolution). So if RE 4 isn't doing that, they yeah the upscaler is probably broken, unless it is just a problem with the M1 GPU family and doesn't have that happen for the others.
You mean 4K with MetalFX should give similar frame rate as native 1080p? Then no! At 1080p I get around 70 fps while as you see above around 48 fps at 4K with Metal FX Quality