There is no package in Workspace to install the AMD Radeon drivers for Debian Stretch (v9.x) or Buster (v10.x) so you will find a manual process bellow to install these drivers.
You can check your Debian version by following instructions in this article:
How to check your operating system version and Caldera compatibility
All actions must be done as root user in the terminal (type "su" in terminal and validate with root password).
1) Update the list of repositories for the Debian packages by editing the file "/etc/apt/sources.list".
To edit the file, type in terminal:
pluma /etc/apt/sources.list
You have to use the repositories specific to your Debian version.
The repositories for Debian Stretch should be:
deb http://deb.debian.org/debian stretch main
deb-src http://deb.debian.org/debian stretch main
deb http://deb.debian.org/debian-security/ stretch/updates main
deb-src http://deb.debian.org/debian-security/ stretch/updates main
deb http://deb.debian.org/debian stretch-updates main
deb-src http://deb.debian.org/debian stretch-updates main
deb http://httpredir.debian.org/debian/ stretch main contrib non-free
The repositories for Debian Buster should be:
deb http://deb.debian.org/debian buster main contrib non-free
deb-src http://deb.debian.org/debian buster main contrib non-free
deb http://deb.debian.org/debian-security/ buster/updates main contrib non-free
deb-src http://deb.debian.org/debian-security/ buster/updates main contrib non-free
deb http://deb.debian.org/debian buster-updates main contrib non-free
deb-src http://deb.debian.org/debian buster-updates main contrib non-free
Disable all other repositories in the file by putting a # symbol in front of their lines.
Warning: Double-check to be sure your are using only the repositories for your Debian version.
Save the changes before exiting the file.
2) Now that the system knows where to look for the packages, you have to download the list of available packages.
To do that type in terminal (still as root):
apt-get update
It should update the packages and indicate that it's done.
If it tells you have there are some duplicate repositories during the process then check in the error message to see in which file and line they are (usually will be in folder /etc/apt/sources.list.d/) and disable them by editing this file (with "pluma" as before) and putting a # symbol in front of these lines.
Do again the update command to be sure all is done correctly after the change.
3) Now you have to download the AMD Radeon drivers.
Type the following line in the terminal as root:
apt-get install firmware-linux-nonfree libgl1-mesa-dri xserver-xorg-video-ati
Validate the installation.
Once it's done reboot the computer with your AMD Radeon card active and the monitor cable plugged on it.