Denon did announce once, a long time ago, that they would be supporting offline storage for Beatport. There was an official statement on the Denon DJ site and another on Beatport.
Unfortunately some time later, Denon removed all evidence of that statement from their site (with no explanation as to why) - but the Beatport one stayed up until fairly recently.
That’s gone now too.
See Beatport link to Engine Dj - #4 by PKtheDJ
Ooh this is still up though: Beatport Link and offline storage coming to Denon DJ hardware | MusicTech
“by the end of 2019” eh? So much for that idea 