Running AMD Radeon HD 7870 XT Tahiti on Ubuntu 20.04 LTS

First of all, I'm new to the Linux world with graphical UIs and I only have some experience in using "headless" terminal only unix varieties. I'm unsuccessfully trying to run an older intel i5-750 computer with an AMD Radeon HD 7870 XT Tahiti PCIE graphics card. I installed a fresh copy of Ubuntu 20.04 LTS with kernel

anni@APOLLON:~$ uname -a
Linux APOLLON 5.8.0-53-generic #60~20.04.1-Ubuntu SMP Thu May 6 09:52:46 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

and on bootup of the computer, after seeing the ubuntu boot logo the screen just shows this weird pattern as shown in the photo below I tested all of the video cards outputs, HDMI, DVI, DisplayPort 1, DisplayPort 2 with the same results. I'm currently running ubuntu in recovery mode without any loaded video drivers without any other problems. The output of lspci is

anni@APOLLON:~$ lspci
...
07:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Tahiti LE [Radeon HD 7870 XT]
...

The hardware is OK as it is running perfectly fine under Windows 10 so it must be a driver/configuration issue I cannot fathom. Does anybody have any clues on what to do to get opengl/mesa grahpics acceleration working? I want to use the computer for some custom accelerated 3D visualization work.