hi!
Even though adding hd pictures as cover art in the tag editor is possible, for some reason after saving the album and then opening it in an external application (groove music, local player, etc.., tried many), the cover art everytime appears somewhat blurry and noisy. Definitely not as the original picture.
Please fix it
cheers 
What was the resolution of the cover art you added? I've added up to 2000x2000px before without issue.
One thing I have seen though is on my mobile device the music software independently generates various sizes of cover art for the music based on the original image, rather than displaying the raw original scaled. Not sure if this may be what is being observed here.
Who should fix it?
What does the picture look like if you open it in MP3tag? Has it changed?
I would say this is a problem of the player that you use.