Oh, I assumed DeX was Samsung's Linux on Galaxy project. What's under the hood with both? What kind of OS is DeX? What kind of DE would Linux on Galaxy run?
DeX is a dock that tells your phone to go to "desktop mode". It is still Android.
With "Linux on Galaxy" I guess you'd be running whatever DE you like. Unless they've done it differently and you're in DeX desktop but can run full Linux apps there. Not sure.
[1] https://seap.samsung.com/linux-on-galaxy