FSR 2.0 is similar to XeSS in the sense that RDNA GPU have a different code path than others cards. Many people complained that they did saw such bad image quality on AMD and after testing it, DF found that image is slightly better. They also acknowledged that they searched super hard to get to a place where this behavior happen (the fuzzy character moving.)
But there, i do not think that it's what causing FSR 2.0 issue here. I suspect they do not have set the Mipmap Bias correctly and the cable we see are texture instead of polygon.
Normally, you get a different level of Mipmap per resolution to get a smooth and clean texture. A texture with too high resolution too far away or in a too low resolution will look very pixelated.
When you want to upscale an image, you want to run the mipmap bias of the resolution you want to upscale or higher so you can extract the pixel you wouldn't see at lower resolution. This one of the way FSR 2.0 and DLSS extract sub pixel details.
You clearly see in the screenshot they selected that the black scratch is disappearing with FSR and that shouldn't happen if the Mipmap level would have been setup properly.
View attachment 252349
If the cable are texture instead of polygon, they would have similar effect.
And if they missed that, who know what they didn't do well too. Doing Temporal upscaling require more work than spatial and if you don't do the prerequisite first, you will have image quality problem.