[HOWTO]: AMD RX 7900 series + Arch + Mesa + Steam
https://www.reddit.com/r/archlinux/comments/zypm56/howto_amd_rx_7900_series_arch_mesa_steam_redux/

[mesa-git]
Server = https://pkgbuild.com/~lcarlier/$repo/$arch
SigLevel = PackageOptional

pacman -S --needed base-devel multilib-devel mesa-git lib32-mesa-git vulkan-radeon-git lib32-vulkan-radeon-git

NOTE: We're installing the packages from Lord Heavy's repo, hence the -git suffixes above.

Finally, to enable early KMS, edit /etc/mkinitcpio.conf and add amdgpu to the MODULES section:

MODULES=(amdgpu)

Update your initramfs:

mkinitcpio -P