Don’t know about specific Arch packages. But for my OpenSUSE experimentations I have gitlab.com/evlaV/linux-integration, steamdeck-packages.steamos.cloud/…/jupiter-main/ and github.com/firlin123/jupiter-dkms bookmarked.

I think the steamos-customizations-jupiter and linux-firmware-neptune-jupiter packages are worth a look. And I recently compiled drivers/hid/hid-steam.c from Valve’s linux sources to get a bugfix for the controller if you run it without Steam.