Please read, we have unofficial repo for manjaro https://nonfree.eu/
GitHub - mesa-freeworld/mesa-nonfree
### install ###
# locally trust the ci key
sudo pacman-key --recv-keys B728DB23B92CB01B && \
sudo pacman-key --lsign-key B728DB23B92CB01B
## add the repo configuration:
sudo sh -c "curl -s https://nonfree.eu/$(pacman-mirrors -G)/ > /etc/pacman.d/mesa-nonfree.pre.repo.conf"
## include the repo configuration:
sudo sed -i '/^\[core\]/i \Include = /etc/pacman.d/mesa-nonfree.pre.repo.conf\n' /etc/pacman.conf