# uname -a
Linux myserver 4.9.0-13-amd64 #1 SMP Debian 4.9.228-1 (2020-07-05) x86_64 GNU/Linux

Please note: this is Devuan, not Debian. I could not find a forum for Devuan. I know there are forums for Devuan, but I cannot login, no matter what I do.

This is a brand new install. I am using MATE.

I am using two monitors, one VGA, the other DVI. I have AMD Radeon graphics.

# lspci -nn | grep VGA
01:05.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] RS780L [Radeon 3000] [1002:9616]

Whenever I search for Devuan, I get Debian.

I found this:

AMD/ATI Drivers (amdgpu, radeon, r128, mach64)
This page describes the process of installing and configuring the display drivers for ATI/AMD graphics hardware on Debian systems.
https://wiki.debian.org/AtiHowTo

I'm not sure if adding debian sources in the sources.list will work.

Any advice appreciated.

I decided that since this is a new install, I would just try the debian repository on my devuan system. Seemed to work. I hope it did not install systemd.

There's little difference between standard Debian and Devuan except for one very significant thing. Debian has a modern init system that some current software depends on. Devuan uses an antique init system that some current software is incompatible with. Installing Debian's video drivers shouldn't be impacted by which init system is in use.

Devuan is Debian, just without the systemd sub system.