You're better to ask CHMultimedia, he has a Tab S5e and he have DEX on it but I don't know how he did that... For Linux on Dex, it's still available here BUT you're better to read this before installing it : https://www.linuxondex.com/
I know this is old, but i just discovered this feature and am downloading the OS right now. I have an S10e. I will let you know how it goes shortly! Stopped me dead in my tracks hunting for a Qualcomm One Ui beta to mod and install. Seems like i won't have use of it in about a month.