The video features are problematic and broken. Cubase 9.5 played video files of various formats perfectly - also have installed the Dnx codec etc.
Now also cannot use Blackmagic Decklink MiniMon 4k card, dead, no picture.
This is exactly what happened with the Nuendo 8.3 update and obviously SB have borrowed that here. Now neither apps are able to use the Decklink. Cubase 10 also will not play vids correctly in a window, stops playback after a few minutes, or choppy, useless etc. For the moment, Nuendo will play OK in a window.