I have a Shield TV Pro and, as long as the display settings are set correctly, it plays Dolby Vision for Disney+ fine. HOWEVER...
You're aware of the number of bits, e.g. 10 bit or 12 bit for HDR and DV? And whether 4:4:2 or 4:4:4 etc etc... there are many different combinations of these (I haven't even touched on here but many more experts on AVforums). You've got the rec 2020 etc etc. There's also the frequency, as some TVs can't do 60Hz!
Basically, I can happily play DV for Netflix. But I can't play some of the titles properly on Disney+ in DV, as some of them are in "higher bits". While the Shield copes with this, it can do 12 bit DV in 4:4:4. My Denon amp (checked in manual) can do this too. BUT either my HDMI leads (maybe) or (more likely) I don't think my Toshiba TV can do it. If I set it to 10 bit rec 2020 in the Shield then it plays.
It takes a lot of messing around with the display settings on the Shield to work out what your TV and HDMI cables and amp can all cope with! The most advanced I have found is Start Wars VIII The Last Jedi... I advise playing that and getting the best setting you can.
Have you tried putting the HDMI directly into the TV, so that you can establish what the amp is limiting on passthrough? When you swap the leads don't forget to power everything off and to turn on TV first... I'm not joking, it makes a difference haha - or at least it does with my setup.