Used Rekordbox and now I use traktor. I only quickly tried it 2 years ago with a DDJ-400 and somehow the mapping was not working correctly. I did not want to fiddle with it at that time. Buy maybe I will give it a go again at some point.
Also, apparently someone used a DDJ-400 as part of a RPi-based standalone setup: https://djtechtools.com/2020/11/05/building-a-standalone-ddj...
Used Rekordbox and now I use traktor. I only quickly tried it 2 years ago with a DDJ-400 and somehow the mapping was not working correctly. I did not want to fiddle with it at that time. Buy maybe I will give it a go again at some point.