Take everything I say down below as an inexperienced user, and to be honest I do not know exactly what each command does, only from what they say from the documentation.
I ended up just messing around with a lot of trial and error to get it to work. So this may or may not work for someone else. I might try this again at some point and do a more thorough documentation.
I ended up also rebooting my PC quite a few times to make sure after each large update it would pick up the new stuff. So I'll document these down too.
------Step 1------
By following this link, scroll down to "Jonathan - joni999" replied message that will provide the answers you need to this problem.
https://discussion.fedoraproject.org/t/blender-amd-and-opencl/40199/8
Basically you want to get "hipcc" which I think is the official HIP libraries for AMD GPUs, by running these commands:
sudo apt install mesa-common-dev
sudo apt install clang
sudo apt install comgr
sudo apt-get -y install rocm-dkms
Reboot the computer
I found this by finding the official documentation from AMD here:
https://rocmdocs.amd.com/en/latest/Installation_Guide/HIP-Installation.html
------Step 2------
In the step 2 of "joni999" message, I came across the same problem as them where it didn't create "/opt/rocm/bin", so I follow the link they provided to install "ROCm".
BUT I followed a slightly different route by using the "upstream kernel drivers" instead, so that it uses the latest drivers. I'll write down my process here. You follow the normal procedure of installing:
(fair warning, the commands below will obviously restart your PC after the update)
sudo apt update
sudo apt dist-upgrade
sudo apt install libnuma-dev
sudo reboot
Then run this:
wget -qO - http://repo.radeon.com/rocm/apt/debian/rocm.gpg.key | sudo apt-key add -
echo 'deb [arch=amd64] http://repo.radeon.com/rocm/apt/debian/ xenial main' | sudo tee /etc/apt/sources.list.d/rocm.list
If you run into warnings, you can ignore them. However if you run into actual errors updating gpg key stuff, or something related to keys being expired, then I believe you can run this:
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys f7f8147431c75e505c58a6f3a3548510869357a6 rocm.gpg.key
(not sure if this above command will work because I didn't run into any actual errors, just simple warnings, but will leave it here just in case)
------Step 3------
Then you proceed to install the actual ROCm development packages instead of the regular "ROCK" version as they call it:
sudo apt update
sudo apt install rocm-dev
Reboot the computer
Now you to need to make sure the actual user account you are using has "group permissions" to use the GPU. Type in:
sudo usermod -a -G video $LOGNAME
I believe you change "$LOGNAME" with the username of your account.
So for me it was "sudo usermod -a -G video dareth"
Now, below you can run this optional commands but I'd recommend adding them just in case, as apparently they'll ensure all future created accounts or users on the PC would have access to the GPU as well:
echo 'ADD_EXTRA_GROUPS=1' | sudo tee -a /etc/adduser.conf
echo 'EXTRA_GROUPS=video' | sudo tee -a /etc/adduser.conf
Now the next command will make it easier for apps to utilize the ROCm.
echo 'export PATH=$PATH:/opt/rocm/bin:/opt/rocm/profiler/bin:/opt/rocm/opencl/bin/x86_64' | sudo tee -a /etc/profile.d/rocm.sh
Reboot the computer
------Step 4------
Everything should work fine now BUT if Blender still does not pick up your AMD GPU under HIP, then try also installing the actual "ROCK" packages on top of the development ones.
sudo apt update
sudo apt install rocm-dkms
Reboot the computer
You GPU should now show up under HIP in Blender after.