reference
https://portal.databasemart.com/kb/a457/how-to-install-desktop-environment-and-xrdp-service-in-debian-9.aspx
1. Make sure you have installed desktops
If not, run the following installation, reboot after installing.
tasksel
2. Install XRDP TigerVNC
apt-get install xrdp tigervnc-standalone-server
3. Start XRDP
systemctl start xrdp
systemctl enable xrdp