Until Nvidia or AMD Radeon offer full support for Open Source, there is sadly no other way of getting the drivers to work than to configure the drivers as outlined below.
The driver you need can be found in this repository:
sudo add-apt-repository ppa:oibaf/graphics-drivers
Then run
sudo apt update
sudo apt -y upgrade
Reboot and test.
Open terminal and run:
lshw -c video
Make sure it says amdgpu. This should answer your question as asked... Everything below may be necessary, however, to get it all configured. You can test how it works without the parameters below, first.
Now, edit your grub with new parameters:
sudo nano /etc/default/grub
Find this line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" and change it to:
GRUB_CMDLINE_LINUX_DEFAULT="radeon.si_support=0 radeon.cik_support=0 amdgpu.si_support=1 amdgpu.cik_support=1 amdgpu.dc=1 amdgpu.dpm=1 amdgpu.modeset=1"
Once that is changed, paste this line to the end of the file:
GRUB_GFXMODE=1920x1080x32
You can change the resolution to whatever you want.
Press ctrl+x to exit, then the y key to say yes to save, then the enter key to save as current configuration.
Run
sudo update-grub
and
sudo update-initramfs
Reboot and test.
If still not quite working right, you may need to blacklist the Kernel Module for Radeon:
sudo nano /etc/default/grub
Add the following line
blacklist radeon
Press ctrl+x to exit, then the y key to say yes to save, then the enter key to save as current configuration.
Then run:
sudo update-initramfs -u
sudo reboot
and test.