The same image run through Gimp 2.8.22 (Win 7) and Gimp 2.10.6 and the only visible difference in the Gimp export PDF is the options Apply layer masks/Convert bitmaps/Omit hidden are off in Gimp 2.8 and on in Gimp 2.10 As far as I know this is the default state. First thing I would try is un-ticking those options in Gimp 2.10 "just-in-case" and try an upload as a test.
Same image out of each, Gimp 2.8 file size is a tiny bit smaller, A quick test and that is those on/off options in play.
The main difference are the versions of poppler and cairo used 1.14 vs 1.15 It could be a bug in either of those. Not much you can do about that. Both Gimps make PDF 1.5 which supports transparency.
last version of Gimp 2.8
https://download.gimp.org/mirror/pub/gim...-setup.exe
Edit: Gimp 2.8 single window mode is bottom of the Gimp Windows menu.
Same image out of each, Gimp 2.8 file size is a tiny bit smaller, A quick test and that is those on/off options in play.
The main difference are the versions of poppler and cairo used 1.14 vs 1.15 It could be a bug in either of those. Not much you can do about that. Both Gimps make PDF 1.5 which supports transparency.
last version of Gimp 2.8
https://download.gimp.org/mirror/pub/gim...-setup.exe
Edit: Gimp 2.8 single window mode is bottom of the Gimp Windows menu.