Ubuntu 20.04 install proprietary AMD driver for Radeon R7 250

Hi guys.

I use Ubuntu 20.04 and I'm not happy with the open source 'radeon' driver, because I can't make crossfire work with this one (correct me if I'm wrong).

I need to install the proprietary driver.

My two graphics are : (from lshw command)

*-pci:0
description: PCI bridge
product: RD890/RD9x0/RX980 PCI to PCI bridge (PCI Express GFX port 0)
vendor: Advanced Micro Devices, Inc. [AMD/ATI]
physical id: 2
bus info: pci@0000:00:02.0
version: 00
width: 32 bits
clock: 33MHz
capabilities: pci pm pciexpress msi ht normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:26 ioport:e000(size=4096) memory:fea00000-feafffff ioport:c0000000(size=268435456)
*-display
description: VGA compatible controller
product: Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]
vendor: Advanced Micro Devices, Inc. [AMD/ATI]
physical id: 0
bus info: pci@0000:01:00.0
version: 00
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
configuration: driver=radeon latency=0
resources: irq:35 memory:c0000000-cfffffff memory:fea00000-fea3ffff ioport:e000(size=256) memory:c0000-dffff
*-multimedia
description: Audio device
product: Oland/Hainan/Cape Verde/Pitcairn HDMI Audio [Radeon HD 7000 Series]
vendor: Advanced Micro Devices, Inc. [AMD/ATI]
physical id: 0.1
bus info: pci@0000:01:00.1
version: 00
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi bus_master cap_list
configuration: driver=snd_hda_intel latency=0
resources: irq:39 memory:fea60000-fea63fff
*-pci:1
description: PCI bridge
product: RD890/RD9x0/RX980 PCI to PCI bridge (PCI Express GPP Port 0)
vendor: Advanced Micro Devices, Inc. [AMD/ATI]
physical id: 4
bus info: pci@0000:00:04.0
version: 00
width: 32 bits
clock: 33MHz
capabilities: pci pm pciexpress msi ht normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:27 ioport:d000(size=4096) memory:fe900000-fe9fffff ioport:b0000000(size=268435456)
*-display
description: VGA compatible controller
product: Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]
vendor: Advanced Micro Devices, Inc. [AMD/ATI]
physical id: 0
bus info: pci@0000:02:00.0
version: 00
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
configuration: driver=radeon latency=0
resources: irq:37 memory:b0000000-bfffffff memory:fe900000-fe93ffff ioport:d000(size=256) memory:fe940000-fe95

I want to make them work in crossfire mode.

With previous versions of Linux, (I used Mageia before) I was able to install the AMD proprietary driver.

I've downloaded the amd-catalyst-13.12-linux-x86.x86_64 driver with this command :

# ./amd-catalyst-13.12-linux-x86.x86_64.run --force

Uncompressing AMD Catalyst(TM) Proprietary Driver-13.251.............................................................................................. .................................................................................................... .................................................................................................... .................................................................................................... .................................................................................................... .................................................................................................... .................................................................................................... .................................................................................................... .................................................................................................... .................................................................................................... .................................................................................................... .....................................................
=====================================================================
AMD Catalyst(TM) Proprietary Driver Installer/Packager
=====================================================================

error: Detected X Server version 'XServer 1.20.9_64a' is not supported. Supported versions are X.Org 6.9 or later, up to XServer 1.10 (default:v2:x86_64:lib:XServer 1.20.9_64a:none:5.4.0-72-generic:)
Installation will not proceed.

I also downloaded the amdgpu-pro-19.20-812932-ubuntu-18.04 but how to force the install? I have plenty .debs in the folder and I would like a command to install them all.

I executed the amdgpu-install as root and I'm stuck with this result :
The following packages have unmet dependencies:
amdgpu-lib32 : Depends: libwayland-amdgpu-client0:i386 (= 1.15.0-812932)
Depends: libwayland-amdgpu-server0:i386 (= 1.15.0-812932)
Depends: libgbm1-amdgpu:i386 (= 1:18.3.0-812932)
Depends: libegl1-amdgpu-mesa:i386 (= 1:18.3.0-812932)
Depends: libegl1-amdgpu-mesa-drivers:i386 (= 1:18.3.0-812932)
E: Unable to correct problems, you have held broken packages.