We've been fooled by worse fakes before, and there have been real pictures that have looked even less convincing and poorer quality than this as well.
If there was a specific image of a Y-20 from this specific angle that this could have been doctored from, it would be a smoking gun, but I doubt we'd find one.
However, it looks like this image is taken from a video app (there seems to be a circular douyin or other shortform video app profile, which is cut out on the right side of the image), so if this is real then perhaps this is just a screenshot of a video.
And if there's a video showing the aircraft in movement -- well it goes without saying that videos are much harder to doctor or fake.
Also, if this is real, the low profile roundel on the fuselage and serial number on the tail corresponds with other Y-20As of late, which we would expect the in service Y-20Bs to be the same.
781 did Really? That image of 781 is well known a PS job by deleting the „0“ … the true number is 7810 and not 781
www.sinodefenceforum.com
Overall, the quality is too poor for us to tell at a glance, so the jury is still out.