Comment 6 for bug 1798091

Hey Jamie, sorry but it seems that issue didn't get fixed, see bug #1799688

The denied error states
name="/tmp/gnome-desktop-thumbnailer.png"

or your rule is
"owner /tmp/{,.}gnome_desktop_thumbnail.* w,"

there is at least a mismatch _ vs - in the filename

but also "thumnail.*" seems to not work, if I replace ".*" by "er.png" (e.g the exact filename) then nautilus starts showing the pdf previews (I tested by copying a pdf as a new bug.pdf name)