The OSRIC Compendium module content (class/race/items/actors/etc...) is included through a module found here.

https://github.com/CelestianGC/osric-compendium

Manifest URL to install the module:

https://github.com/CelestianGC/osric-compendium/releases/latest/download/module.json

Paste the Manifest URL and click Install

(Once the module is enabled you'll have the ActorCompendiums and Adventure you can install)