Polychromatic is available from the AUR. For example, using an AUR helper:
yay -S polychromatic
Use polychromatic-git instead for the latest features, fixes and improvements from the master branch.
For example, using an AUR helper:
yay -S polychromatic-git
Depending on the AUR helper, you may need to manually update/rebuild this package if you wish to get the latest changes.
Next up, OpenRazer
Polychromatic is just a frontend. If you haven't already, you'll need to install this driver and daemon: