Wallpaper is blurry on 4K monitor when Window Scaling = 2x
On a Dell U2720Q monitor with resolution 3840x2160, the wallpaper looks more blurry when I set Window Scaling = 2x in Appearance; the same bug occurs with environment variable GDK_SCALE=2. I'm using https://eoimages.gsfc.nasa.gov/images/imagerecords/144000/144898/BlackMarble_2016_01deg.jpg as the wallpaper. Here's part of what it looks like at 1x:
and here's the same part when Window Scaling is 2x:
I've set the "Style" as "Stretched" in the Desktop setting and the aspect ratio is correct; it's just that the wallpaper looks more blurry with 2x. Something seems to have downsampled the image when it shouldn't. "Scaled" and "Zoomed" have the same problem.
I'm using stock xfdesktop-4.14.3 with Fedora 32, the nvidia 455.45.01 driver from rpmfusion, and a Geforce GT 1030 card. I've also found the bug reported at https://www.reddit.com/r/xfce/comments/cjr1a2/low_res_wallpaper/ and https://www.reddit.com/r/archlinux/comments/cunatp/hires_wallpaper_blurry_xfce/, but there doesn't seem to be any solution.