it seems that the "2018" version have no Atmos (search the keyword "atmos")
https://cordcuttingreport.com/2018/10/18/mi-box-review/
https://www.flatpanelshd.com/news.php?subaction=showfull&id=1539147219
"2016" version have atmos
https://forum.kodi.tv/showthread.php?tid=275083
however, i can't guarantee that the source are correct as the information about atmos on this device is hard to find