New Functionality in 3DPlay Which says"A mixed reality experience (with limited functionality) is now available in the Scenario Chooser with a HoloLens device". You can found it through the link:https://help.3ds.com/2021x/English/DSDoc/X3dplayUserMap/X3DPlay-r-wn.htm?ContextScope=cloud at User Assistance R2021x. 
I didn't succeed in the test. and I have updated to R2021X HF 3.15. I'm very interested in the new feature and look forward to receiving suggestions from anyone in the community if you know more about it.