How to INSTALL last AMD Radeon card driver on Ubuntu Mate 20.04 LTS?

Hi!

With the OpenSource AMDGPU kernel driver, my Radeon 5600XT works.

But I can not make any settings because the AMD Radeon Software/Driver center is not available.

I can't get AMD Radeon card driver from the AMD webpage to work.
(https://www.amd.com/en/support/kb/release-notes/rn-amdgpu-unified-linux-20-45)

Kernel:
5.4.0-58-generic

After installing the AMD Radeon card driver and setting the driver to "amdgpu" in xorg.conf, I rebooted my system.

After that, error:

[FAILED] Failed to start Detect the available GPU and deal with system changes.
[FAILED] Failed to start Light Display Manager.

With my NVIDIA card, I have no errors.

After that, I tried to install the AMDGPU-pro driver.

Shortly before the AMDGPU-pro driver was finished, an error message came up that some packages need at least kernel 5.6.

Do I really need the xorg.conf for the
AMD OpenSource kernel GPU driver? (amdgpu)

I am on kernel 5.4.0-58.

What can I do to get the AMD Radeon driver for AMD Radeon 5600XT card to work in Ubuntu-Mate 20.04 LTS?

Where is the AMD GPU Driver/Software center after driver install?
How do I make tweaks to the graphics card?
How to edit color settings?

I need the setting "DIGITAL vibrance/saturation"

Please help, thanks!