I have added support for system-wide plugin installations in Linux for the upcoming 1.0 release. The plugin files can be installed system-wide to the /usr/lib/openrgb/plugins path, which allows them to be provided by distribution packages rather than manually downloading them.
I have created AUR packages for the following plugins and they have been picked up by the Chaotic AUR repository if you want binary builds.
openrgb-plugin-e131-receiver-git
openrgb-plugin-effects-git
openrgb-plugin-hardware-sync-git
openrgb-plugin-visual-map-git
I plan to update the rest of the plugins on https://gitlab.com/OpenRGBDevelopers and get them into the AUR as well before 1.0 releases. Until that happens, you will need to use the openrgb-git AUR package to utilize these new plugin packages. The current 0.9 release in the main repository does not support system-wide plugin installation.